Mostrar código-fonte de Testwiki:Texto alternativo para imagens

{{Recomendação|WP:ALT}}
Um [[Atributo alt|texto alternativo ou substituto]] (texto alt) é utilizado para substituir uma imagem, quando a imagem não puder ser vista. Toda imagem visível deve possuir um texto alternativo, a menos que ela seja ''puramente decorativa'', isto é, ela não tem função é utilizada apenas para formatação visual ou decoração.<ref>{{citar web|url=http://www.w3.org/QA/Tips/altAttribute.html |título=Use the <code>alt</code> attribute to describe the function of each visual |autor=Hazaël-Massieux D |data=2007-05-28 |acessodata=2009-07-06 |trabalho=W3C Quality Assurance Tips for Webmasters }}</ref> O texto alternativo deve ser conciso e deve enfatizar os aspectos visuais mais importantes da imagem: ele deve resumir a essência da imagem ao invés de descrevê-la detalhadamente. Seu público alvo consiste em deficientes visuais que utilizam [[tecnologia assistida]] tal como [[leitor de tela|leitores de tela/ecrã]]. O texto também deve fazer sentido em qualquer navegador gráfico no qual a apresentação de imagens é desativada, e ele deve se adequar com o texto a sua volta quando visualizado em um navegador web textual.

Na Wikipédia, as imagens tipicamente agem como ligações e, portanto, necessitam o texto alternativo, que é especificado com um parâmetro "<code>alt=</code>". Aqui está um exemplo da [[Ajuda:Guia de edição/Como usar imagens|marcação wiki]] para uma imagem com o texto alt text, próximo ao que a imagem se assemelha no seu navegador.

{|  style="float:right; caption-side:bottom;"
|+ style="font-style: italic; font-size: 78%; line-height: 1.3em; margin-left: 2em;" | Se você está usando um navegador gráfico padrão e quer ler o texto alt dessa imagem, solicite ao navegador para ele apresentar as propriedades da imagem.
|-
| [[Ficheiro:Dannebrog.jpg|thumb |alt=No céu flamula uma bandeira vermelha com uma cruz branca vertical, cuja barra vertical é deslocada na direção do mastro. |A [[bandeira nacional]] mais velha ainda em uso é a da [[Dinamarca]] do século XII, a [[Bandeira da Dinamarca|''Dannebrog'']].]]
|}
<blockquote><code><nowiki>
[[Image:Dannebrog.jpg|thumb |alt=No céu flamula uma bandeira vermelha com uma cruz branca vertical, cuja barra vertical é deslocada na direção do mastro. |A [[bandeira nacional]] mais velha ainda em uso é a da [[Dinamarca]] do século XII, a [[Bandeira da Dinamarca|''Dannebrog'']].]]
</nowiki></code></blockquote>

Neste exemplo, retirado do artigo [[bandeira]], um leitor de tela lerá o seguinte texto:
:"Link no céu flamula uma bandeira vermelha com uma cruz branca vertical, cuja barra vertical é deslocada na direção do mastro. A link bandeira nacional mais velha ainda em uso é a da link Dinamarca do século XII, a link Dannebrog."
Se a marcação wiki não possuir o texto alt, o leitor de tela lerá, "Link ficheiro dois pontos Dannebrog ponto jota pê gê. A link bandeira nacional mais velha ainda em uso é a da link Dinamarca do século XII, a link Dannebrog." Isso daria nenhuma informação  sobre a aparência da imagem.

Texto alt não é o mesmo que uma [[Wikipedia:Legendas|legenda]]. '''Texto alternativo tem como alvo aqueles que não podem ver a imagem, enquanto a legenda é voltada para todos os leitores.''' Em geral, o texto alternativo resume a aparência da imagem, enquanto a legenda auxilia todos os leitores a interpretarem a imagem, com foco em seus elementos mais essenciais e para conectar ela com o texto do artigo.

== Objetivo ==

Textos alternativos atua como um substituto para uma imagem, para aqueles que não podem vê-la. Em contraste com as legendas, que são escritas para todos. O texto alt quase nunca é um substituto perfeito para a imagem ou uma descrição exaustiva da mesma; a intenção é apenas que o texto alt seja funcional, de modo que seja muito melhor do que nada para seus leitores. Navegadores que exibem o texto alt normalmente, fazem-o antes da legenda, então, uma boa prática é colocar texto alternativo antes da legenda na [[Ajuda:Guia de edição/Como usar imagens|sintaxe de inserção de imagens da Wikipédia]]. Aqui está um exemplo retirado da introdução de ''[[Ptolomeu II Filadelfo]]'', com quebras de linhas para que pudesse ser apresentada aqui:
{{-}}
[[Imagem:Oktadrachmon Ptolemaios II Arsinoe II.jpg|thumb|alt=Uma moeda de ouro com o busto de um homem e uma mulher gorda, emparelhados e perfilados. O homem está a frente e usa uma tiara e drapeados. Na parte superior da moeda está a palavra "ΑΔΕΛΦΩΝ".|Moeda do século III a.C. retratando a co-governantes do Egito ptolemaico: Ptolomeu II (a frente), e sua irmã e esposa de [[Arsínoe II do Egito|Arsínoe II]]. A inscrição em grego ''adelfon'' significa "irmãos".]]
<blockquote><code><nowiki>
[[Imagem:Oktadrachmon Ptolemaios II Arsinoe II.jpg|thumb|alt=Uma moeda de ouro com o busto de um homem e uma mulher gorda, emparelhados e perfilados. O homem está a frente e usa uma tiara e drapeados. Na parte superior da moeda está a palavra "ΑΔΕΛΦΩΝ".|Moeda do século III a.C. retraaando a co-governantes do Egito ptolemaico: Ptolomeu II (a frente), e sua irmã e esposa de [[Arsínoe II do Egito|Arsínoe II]]. A inscrição em grego ''adelfon'' significa "irmãos".]]
</nowiki></code></blockquote>

Textos alternativos são úteis, por exemplo, quando alguém:

* utiliza um [[leitor de tela]]/ecrã como JAWS ou ORCA (''e.g.'', deficientes visuais)
* utiliza navegadores textuais como [[Lynx (navegador)|Lynx]] (''e.g.'', navegadores de telefones móveis)
* utiliza um navegador gráfico com as imagens desabilitadas
* não deseja baixar as imagens
* navega os resultados de uma pesquisa Web
* não consegue descarregar as imagens por problemas na conexão.

Deficientes visuais são o público alvo dos textos alternativos. A ausência de textos alt ou deviso a sua baixa qualidade é uma das maiores causas de frustrações de pessoas cegas na web.<ref>{{citar periódico|autor =Lazar J, Allen A, Kleinman J, Malarkey C |ano=2007 |título=What frustrates screen reader users on the web: a study of 100 blind users |periódico=Int J Hum Comput Interact |volume=22 |número=3 |páginas=247–69 |doi=10.1080/10447310709336964 }}</ref> Um estudo de 2008 sobre acesso de deficientes visuais a Wikipedia listou a falta de texto alt como o primeiro obstáculo.<ref>{{citar conferência|autor =Buzzi M, Leporini B |ano=2008 |título=Is Wikipedia usable for the blind? |títulolivro=Proc 2008 W4A |local=Beijing |páginas=15–22 |doi=10.1145/1368044.1368049 }}</ref> Assim como os demais leitores, os deficientes visuais possuem diferentes necessidades, e o texto deve ser escrito tendo isso em mente. Por exemplo, relativamente pouco desses leitores são cegos de nascença: a grande maioria perdeu sua capacidade visual devido a degenerações relacionadas a idade, e esta maioria compreende termos visuais comuns bem.

Texto alternativo também é utilizado para outros propósitos. Por exemplo, o sistema de busca de imagens do [[Google]] utiliza-a para ajudar a apresentar as imagens apropriadas.

== Essência ==

O texto alt deve comunicar a essência da imagem, isto é, o aspecto geral da imagem. A essência de uma imagem pode incluir qualquer um de seus aspectos visuais, incluindo composição, estilo e iconografia. Começando por descrever os aspectos mais marcantes da imagem e, em seguida cobrindo todos os detalhes importantes, aproximadamente na ordem em que um observador veria numa primeira vez. Por ser um texto geralmente lido em voz alta, e pode ser interrompido se o leitor desejar não escutá-lo, o texto inicial é o que mais provavelmente será lido.

{| class="wikitable"
|+ Capture a essência de uma imagem.
! Contexto !! Imagem !! Texto alt inadequado !! Texto alt adequado
|-
<!--
| As seções [[Beatles#Abbey Road, Let It Be and breakup|Abbey Road'','' Let It Be ''and breakup'']] de ''[[Beatles]]''
| [[Ficheiro:3 Savile Row.jpg|thumb|upright|center|alt=A terrace building. Its ground floor has plaster render inscribed to look like stone, the middle three are red brick, and the top is an attic. Each floor has four sash windows with a dozen or more panes each, except that the bottom floor has a door in place of the second window.|Apple Building at 3 Savile Row, site of the ''Let It Be'' rooftop concert]]
| A small aerial sprouts at the junction between a building and its neighbor. The sun shines brightly on the aerial. Nobody is in sight, except for a dim figure in a van's driver seat. The van is parked in front of the building.
| A terrace building. Its ground floor has plaster render inscribed to look like stone, the middle three are red brick, and the top is an attic. Floors have four sash windows with a dozen or more panes each, except that the bottom floor has a door in place of the second window.
|-
-->
| Artigo sobre [[Milia]]
| [[Image:Milia big.png|thumb|upright|center|[[Milia]]|alt=Lesões na pele extremamente pequena, preenchidas com um material branco, sobre uma pálpebra de um adulto]]
| Examplo de milia
| Lesões na pele extremamente pequena, preenchidas com um material branco, sobre uma pálpebra de um adulto
|}
=== Retratos ===

O texto alternativo para retratos deve começar com qual parte da pessoa é ilustrada, e então informando o sexo, idade aparante ou outro atributo evidenciado em uma primeira vista. Ele pode, então, listar qualquer detalhe que é importante ou óbvio numa observação um pouco mais cuidadosa da imagem. Detalhes casuais, como em que direção a pessoa está olhando, muitas vezes não vale a pena mencionar, pois transmitem pouca informação sobre a aparência da pessoa. Use formulação neutra, ao descrever a aparência da pessoa, tomando cuidado em particular, ao descrever pessoas vivas; por exemplo, raça e deformidades físicas podem ser detalhes sensíveis. A primeira imagem num artigo devotado a uma pessoa geralmente é mais detalhada, para transmitir uma ideia precisa de como a pessoa se parece. Imagens posteriores no mesmo artigo podem ter um texto alternativo resumido, pois se presume que o leitor já conhece o texto descritivo da primeira imagem.

{| class="wikitable"
|+ Dizer como uma pessoa se parece
! Contexto !! Imagem !! Texto alt inadequado !! Texto alt adequado
|-
| Primeira imagem de ''[[Mary Bartelme]]''
| [[Imagem:Mary-Margaret-Bartelme-Bain.jpeg|thumb|upright|center|alt=Cabeça e ombros de uma mulher séria em seus quarenta anos, com cabelo escuro e em um vestido com gola alta de renda alta e um camafeu em seu pescoço, estilo edwardiano|Bartelme por volta de 1913]]
| Fotografia preta e branca, tirada em um estúdio, de alguém cuja cabeça está olhando para a esquerda e seu corpo está a um ângulo de 45 graus.
| Cabeça e ombros de uma mulher séria em seus quarenta anos, com cabelo escuro e em um vestido com gola alta de renda alta e um camafeu em seu pescoço, estilo edwardiano
|-
| Primeira imagem de  ''[[Adelaide Anne Procter]]''
| [[Imagem:Adelaide Anne Procter by Emma Gaggiotti Richards.jpg|thumb|upright|center|alt=Retrato 3 por 4 de uma mulher magra por volta dos 30 anos, vestida de preto. Seus olhos profundos fitam o telespectador. Seu cabelo escuro e liso é partido ao meio, sem uma franja, e o penteado cobre as orelhas, sendo esticado na direção de suas costas.|Retrato não datado por Emma Gaggiotti Richards]]
| Retrato da poetisa e filantropista inglesa Adelaide Anne Procter, mostrando uma mulher em um vestido do século XIX olhando diretamente para o fotógrafo.
| Retrato 3 por 4 de uma mulher magra por volta dos 30 anos, vestida de preto. Seus olhos profundos fitam o telespectador. Seu cabelo escuro e liso é partido ao meio, sem uma franja, e o penteado cobre as orelhas, sendo esticado na direção de suas costas.
|}

=== Diagramas ===

O texto alternativo para diagramas deve transmitir a essência da informação diagramada, tal como o relacionamento entre os objetos diagramados. Ele não deve conter informações não importantes como detalhes decorativos. Se um diagrama contem um texto proeminente, o texto alternativo deve transcrevê-lo.
<!--
{| class="wikitable"
|+ Transmitir as informações de um diagrama, não os detalhes visuais
! Contexto !! Imagem !! Texto alt inadequado !! Texto alt adequado
|-
| rowspan=2 | Seção ''[[fluoretação da água#Mecanismo|Mechanismo]]'' de ''[[fluoretação da água]]''
| rowspan=2 | [[Imagem:Enamel-fluoride-remineralization.svg|thumb|upright|center|alt=Carbonated hydroxyapatite enamel crystal is demineralized by acid in plaque and becomes partly dissolved crystal. This in turn is remineralized by fluoride in plaque to become fluoroapatite-like coating on remineralized crystal.|Demineralization and remineralization of dental enamel in the presence of acid and fluoride in saliva and plaque fluid]]
| Diagrama de como o flúor ajuda a prevenir cáries.
| rowspan=2 | Carbonated hydroxyapatite enamel crystal is demineralized by acid in plaque and becomes partly dissolved crystal. This in turn is remineralized by fluoride in plaque to become fluoroapatite-like coating on remineralized crystal.
|-
| Diagrama: Cristal esmaltado com carbonato de hidroxipatito (em um hexágono amarelo), conectado connected by a pink arrow labeled "Demineralization: Acid in plaque" (in red box) to partly dissolved crystal (in fuzzy pink hexagon), which in turn is connected by a light-blue arrow labeled "Remineralization: Fluoride in plaque" (in blue box) to fluoroapatite-like coating on remineralized crystal (in solid light-blue hexagon).
|}
-->
=== Mapas ===

Assim como os diagramas, os mapas devem ter textos alternativos que elucidam a essência da informação útil neles contidas para o leitor, ao invés de detalhes detalhados como cores e orientação. Se o restante do artigo assume conhecimento do mapa, seu texto deve ser razoavelmente detalhados; do contrário, o texto alternativo pode dar simplesmente uma visão geral sobre o que o mapa diz.

{| class="wikitable"
|+ Dizer o que mapas dizem sobre territórios mapeados.
! Contexto !! Imagem !! Texto alt inadequado !! Texto alt adequado
|-
| A seção ''[[Mumbai#Geografia|Geografia]]'' de ''[[Mumbai]]''
| [[Imagem:Bombaycitydistricts.png|thumb|upright|center|alt=Mumbai é uma estreita península no sudoeste da Ilha Salsette, que se localiza entre o Mar Árabe ao este, Thane Creek ao leste, e Vasai Creek ao norte. O distrito suburbano de Mumbai ocupa a maior parte da ilha.|Mapa de Mumbai]]
| Um mapa da cidade indiana de Mumbai marcada pelas cores amarelo e verde
| Mumbai é uma estreita península no sudoeste da Ilha Salsette, que se localiza entre o Mar Árabe ao este, Thane Creek ao leste, e Vasai Creek ao norte. O ditrito suburbano de Mumbai ocupa a maior parte da ilha.
|-
| A seção ''[[Batalha de Grand Port#Battle|Batalha]]'' de ''[[Batalha de Grand Port]]''. Aqui, o texto adjacente descreve a geografia da balha em alguns detalhes.
| [[Imagem:Battle of Grand Port.svg|thumb|center|alt=Diagrama da batalha ilustrando as posições dos navios britânicos e franceses em relações a margem como descrita no texto.|Plano da batalha. Navios franceses estão em azul, e os britânicos em vermelho.]]
| Navios azuis (ao oeste) e navios vermelhos (ao leste) manobram em uma baia entre Pointe Destiny até o sul e de Vieux Grand-Port para o norte. Os navios vermelhos seguem um canal de água profunda, precorrendo desde Île de la Passe no leste até Vieux Grand-Port; os navios azuis estão onde o canal se abre.
| Diagrama da batalha ilustrando as posições dos navios britânicos e franceses em relações a margem como descrita no texto
|}

{{Mapa de localização|País de Gales
 |lat=51.80893
 |long=-2.71938
 |rótulo=Monmouth
 |position=left
 |alt=Localizada um pouco ao norte da borda sudoeste do País de Gales, na fronteira com a Inglaterra. País de Gales está no centro oeste da Grã-Bretanha.
 |legenda=Localização de Monmouth no[[País de Gales]]
}}
Algumas predefinições como {{tl|Mapa de localização}} geram automaticamente, por padrão, o texto alternativo, mas tipicamente esse texto não é útil para deficientes visuais, e é aconselhável sobrescrever o texto padrão por outro utilizando o parâmtro  "<code>alt</code>". Por exemplo, na caixa de informação do artigo ''[[Monmouth]]'',
<pre style="overflow:auto;">
{{Mapa de localização|País de Gales
 |lat=51.80893
 |long=-2.71938
 |rótulo=Monmouth
 |position=left
 |alt=Localizada um pouco ao norte da borda sudoeste do País de Gales, na fronteira com a Inglaterra. País de Gales está no centro oeste da Grã-Bretanha.
 |caption=Localização de Monmouth no [[País de Gales]]
}}
</pre>

<!--
Clickable maps, such as those generated by {{tl|Location map+}}, need alt text for the map itself (to describe the gist of the overall map), along with alt text for each clickable image within the map. For example, the {{para|link}} parameter of {{tl|Location map~}} creates a clickable image, and so should be used only with a corresponding {{para|alt}} parameter.
{{-}}
-->

=== Galerias ===

Galerias de imagens são algumas vezes apropriadas para artigos. Infelizmente, a [[Wikipedia:Marcação galleria|marcação <code><nowiki><gallery></nowiki></code>]], uma forma fácil de gerar uma galeria, não suporta atualmente textos alternativos. O[[bugzilla:18682|bug Wikimedia 18682]] solicita que essa opção seja adicionada.

=== Vídeos e animação ===

O texto alternativo para vídeos e animações deve descrever brevemente todo o trabalho, não apenas a imagem inicial. As a full description typically requires too much length for alt text, it is good practice to put it in the ''Summary'' section of the file page; see ''[[#Brevity|Brevity]]''.

Some readers are hearing-impaired and others use browsers without audio, so the alt text should not assume that the reader can hear a video. Prominent and brief words in the audio can be transcribed in the alt text, and it is helpful to provide a full transcript of the audio in the video's file description page.
<!--
{| class="wikitable"
|+ Give the gist of all of a video or animation.
! Context !! Image !! Flawed alt text !! Better alt text
|-
| The ''[[International Space Station#Assembly and structure|Assembly and structure]]'' section of ''[[International Space Station]]''
| [[File:January 2009 ISS tour.ogg|thumb|center|[[Expedition 18]] commander [[Michael Fincke]]'s video tour of the habitable part of the ISS from January 2009|alt=A video touring the interior of the space station. Beginning at the forward end of Node 2, the tour shows PMA-2, the Japanese Experiment Module, the Columbus and Destiny laboratories, followed by Node 1 and the Quest airlock. The tour then proceeds through PMA-1 and into the Russian segment, visiting the FGB, a docked Soyuz spacecraft, Docking Compartment, Service Module and two Progress spacecraft.]]
| An assortment of hard-to-make-out equipment arranged at odd angles. In the front is a horizontal black slab with blue patches.
| A video touring the interior of the space station. Beginning at the forward end of Node 2, the tour shows PMA-2, the Japanese Experiment Module, the Columbus and Destiny laboratories, followed by Node 1 and the Quest airlock. The tour then proceeds through PMA-1 and into the Russian segment, visiting the FGB, a docked Soyuz spacecraft, Docking Compartment, Service Module and two Progress spacecraft.
|-
| The lead image of ''[[Territorial evolution of Canada]]''
| [[Imagem:Canada provinces evolution 2.gif|thumb|center|alt=When Canada was formed in 1867 its provinces were a relatively narrow strip in the southeast, with vast territories in the interior. It grew by adding British Columbia in 1871, P.E.I. in 1873, the British Arctic Islands in 1880, and Newfoundland in 1949; meanwhile, its provinces grew both in size and number at the expense of its territories.|Animation of the evolution of the borders and names of Canada's provinces and territories]]
| Animation showing the various map evolutionary stages as detailed in the article Territorial evolution of Canada on Wikipedia
| When Canada was formed in 1867 its provinces were a relatively narrow strip in the southeast, with vast territories in the interior. It grew by adding British Columbia in 1871, P.E.I. in 1873, the British Arctic Islands in 1880, and Newfoundland in 1949; meanwhile, its provinces grew both in size and number at the expense of its territories.
|}
-->
=== Fórmulas matemáticas ===

O texto alt pode ser especificado para fórmulas matemáticas como um atributo da marcação <code>math</code>, dotado de marcações de citação. Por exemplo:
<blockquote><code><nowiki>
<math alt="Raiz quadrada de pi">\sqrt{\pi}</math>
</nowiki></code></blockquote>
gera a fórmula <math alt="Raiz quadrada de pi">\sqrt{\pi}</math> cujo texto é "Raiz quadrada de pi". Para fórmulas simples como essa, uma tradução direta para o português fornece uma descrição curta e não ambígua. Em exemplos complexos, o texto alternativo é geralmente a própria marcação em si, sendo então aceitável e recomendável sua omissão. Por exemplo:

<blockquote><code><nowiki>
<math>\phi_n(\kappa) = \frac{1}{4\pi^2\kappa^2} \int_0^\infty \frac{\sin(\kappa R)}{\kappa R} \frac{\partial}{\partial R} \left[R^2\frac{\partial D_n(R)}{\partial R}\right]\,dR</math>
</nowiki></code></blockquote>

contem nenhum atributo "<code>alt="</code>, e gera:

: <math>\phi_n(\kappa) = \frac{1}{4\pi^2\kappa^2} \int_0^\infty \frac{\sin(\kappa R)}{\kappa R} \frac{\partial}{\partial R} \left[R^2\frac{\partial D_n(R)}{\partial R}\right]\,dR</math>

onde o texto alternativo é simplesmente a marcação:

<blockquote>
\phi_n(\kappa) = \frac{1}{4\pi^2\kappa^2} \int_0^\infty \frac{\sin(\kappa R)}{\kappa R} \frac{\partial}{\partial R} \left[R^2\frac{\partial D_n(R)}{\partial R}\right]\,dR
</blockquote>

<!--
[[meta:Help:Preferences#Rendering math|User preferences]] can affect how math is displayed. Depending on these preferences, simple formulas may be rendered as text instead of as an image. For example, <code><nowiki><math alt="x squared">x^2</math></nowiki></code> generates a formula <math alt="x squared">x^2</math> that is often displayed as text rather than as an image. Since users can set a preference to always generate images for math-mode formulas, a formula's alt text can appear along with an image rendered on a user's browser, even if the formula happens to be rendered as text in your browser. Therefore, if alt text would be useful for a formula, it is helpful to supply the alt text even if that formula happens to display as text on your browser.

Alt text is not used with math formulas that are always rendered as text, such as formulas generated by the {{tl|math}} template.
=== Chemistry ===

If an image contains a simple [[molecular formula]] such as "CH<sub>4</sub>" that cannot be copied directly into alt text because it uses [[Subscript and superscript#HTML|HTML subscripts and superscripts]], it can be represented in alt text using the typographically simpler "CH4" or by the common name "methane".

[[IUPAC nomenclature]] is a standard way to textually describe a complicated [[structural formula]]. There is typically little point to reproducing just the naive visual aspect of such a formula, as it would not convey the image's essence to readers who know little of chemistry, and it would hurt readers who know something of the subject. This is a partial exception to the general rule that alt text should be verifiable by a non-expert; in chemical formulas the reader can be presumed to understand the syntax of the formulas even if expertise in the article's topic is not presumed.

{| class="wikitable"
|+ Use IUPAC nomenclature for complicated structural formulas.
! Context !! Image !! Flawed alt text !! Better alt text
|-
| ''[[Linezolid#Chemistry|Chemistry]]'' section of ''[[Linezolid]]''
| [[Image:Linezolid showing oxazolidinone pharmacophore.svg|thumb|center|alt=Skeletal formula of N-{[(5S)-3-[3-fluoro-4-(morpholin-4-yl)phenyl]-2-oxo-1,3-oxazolidin-5-yl]methyl}acetamide, highlighting the morpholino and fluoro groups in orange, with the rest in blue. The carbon atoms of the parent chain are numbered.|Numbered structure of linezolid, showing the [[pharmacophore]] required for good activity (in blue) and desirable structural features (in orange).]]
| Starting with an orange hexagon outline with O and N at opposite ends, the N is connected via another line to a blue hexagon outline with alternate sides written with double lines. A near corner of the blue hexagon is connected via an orange line to an orange F. The far corner of the blue hexagon is connected via a blue line to a blue pentagon outline with N at the near corner and O at one far corner. Between N and O is a double link to another O. The other far corner of the pentagon is connected via an opening wedge to a line and then to an N next to an H; the N is connected by a line to a junction with a line going one way and a double line to an O going another.
| Skeletal formula of N-{[(5S)-3-[3-fluoro-4-(morpholin-4-yl)phenyl]-2-oxo-1,3-oxazolidin-5-yl]methyl}acetamide, highlighting the morpholino and fluoro groups in orange, with the rest in blue. The carbon atoms of the parent chain are numbered.
|}

== Context ==

[[Imagem:HH Polizeihauptmeister MZ.jpg|frameless|upright|border|right|alt=Half-length portrait of an older policeman. He has a well-trimmed gray mustache, carries a two-way radio, and wears glasses and a dark blue uniform with police hat.]]
Alt text depends heavily on context. Alt text that may be good for an image's occurrence in one article may not be appropriate for a different occurrence. Whether a visual aspect or detail is important enough to appear in alt text depends on the context. For example, the alt text of the image at right might focus on the color of the officer's uniform in ''[[Blue]]'', on the officer's hat in ''[[Peaked cap]]'', and on the stone lion in ''[[Public art]]''.

Although alt text can use lively language to describe the essence of the image, it should not creatively interpret the image, suggest non-obvious meanings, justify the image's importance or significance, or describe its [[provenance]] or how it was created. Those roles are part of the image's context, and they belong to the caption or other nearby text, because sighted readers should see them too.

=== Flow ===

Alt text should make sense in the absence of the image. It should sit comfortably in the flow of the article and be punctuated correctly. One way to review an article with [[screen reader]]s in mind is to read it aloud, including alt text and captions, listening for unwanted repetitions and awkward juxtapositions of sounds.

A helpful way to think about alternative text is to imagine that the Web page text, including all alternative text, is the script for a radio broadcast. Your listeners are not necessarily blind, so they may be interested in hearing about what something looks like. But they cannot possibly see any images via radio, so referring to an image itself will sound silly. If you write your alternative text with this in mind, it should work well.

=== Punctuation ===

Alt text should be punctuated much as captions are, so that it is read naturally by a screen reader. Sentences should be capitalized and terminated with periods as usual. If the alt text is a non-sentence, such as "White flag with central red circle", it should not have a final period. If it is a non-sentence followed by a sentence, the non-sentence should be followed by a period to separate it from the sentences: for example, "Closeup of inflorescence. A bee feeds on orange opened flowers."

=== Proper names ===

Alt text typically should not name people or objects in an image. When in doubt, assume that an entity is not iconic, and needs to be named in the caption or nearby article text. For example, [[Vladimir Putin]] and the [[Guggenheim Museum Bilbao]] are both famous, but they are not so famous that one can reasonably expect an English Wikipedia reader to know what they look like, so alt text should describe their appearance rather than give their names, and they should be named in the caption or other text. In the following examples, a typical reader cannot tell merely from viewing the first image that it is of the [[SMS Helgoland|SMS ''Helgoland'']], or that it is carrying out maneuvers, or that it is in the [[German Bight]], and in the second image typical English-language readers are not expected to know what Putin looks like.

{| class="wikitable"
|+ Omit proper names from alt text, unless they name iconic figures.
! Context !! Image !! Flawed alt text !! Better alt text
|-
| First image of [[SMS Helgoland|''SMS'' Helgoland]]
| [[Imagem:Bundesarchiv DVM 10 Bild-23-61-09, Linienschiff "SMS Helgoland".jpg|thumb|center|alt=Large gray battleship at sea. Dark smoke streams back from its three closely arranged funnels.|SMS ''Helgoland'' {{circa|1911–1917}}]]
| The SMS "Helgoland", carrying out maneuvers in the German Bight
| Large gray battleship at sea. Dark smoke streams back from its three closely arranged funnels.
|-
| ''[[Pavel Bure#Personal life|Personal life]]'' section of ''[[Pavel Bure]]''
| [[Imagem:Vladimir Putin in the United States 13-16 November 2001-20.jpg|thumb|center|alt=Four men in suits, two middle-aged and two in their thirties, sit smiling around a glossy wood table. A photographer hovers in the background.|Bure (second from right) along with his brother Valeri Bure (far right) and Russian Olympic Committee President Leonid Tyagachev (second from left), meet with Russian President Vladimir Putin (far left) on November 14, 2001.]]
| Vladimir Putin, another middle-aged man, and two hockey players sit smiling around a glossy wood table. A photographer hovers in the background.
| Four men in suits, two middle-aged and two in their thirties, sit smiling around a glossy wood table. A photographer hovers in the background.
|}

A few people and things are so famous that one can reasonably expect a typical reader of English Wikipedia to know what they look like. Examples include Big Ben, the Eiffel Tower, the White House, Gandhi, Jesus, Lincoln, Mao, and Napoleon. However, the first image in an article devoted to a famous person or thing should provide a relatively detailed visual description of it, as that is the most plausible place where a visually impaired reader might want to know details about appearance.

{| class="wikitable"
|+ Assume knowledge of what a truly famous entity looks like, except in the entity's own article.
! Context !! Image !! Flawed alt text !! Better alt text
|-
| The large ''[[Jacques-Louis David#Gallery|Gallery]]'' section of ''[[Jacques-Louis David]]''
| rowspan=2 | [[Image:Jacques-Louis David 017.jpg|thumb|upright|center|alt=Full length portrait of Napoleon standing|''[[The Emperor Napoleon in His Study at the Tuileries|Napoleon in His Study]]'' (1812), [[National Gallery of Art]], Washington, D.C.]]
| rowspan=2 | David's painting
| Full length portrait of Napoleon standing
|-
| First image in ''[[Napoleon]]''
| Full length portrait of a man in his forties, in high-ranking dress white and dark blue military uniform. He stands amid rich 18th-century furniture laden with papers, and gazes at the viewer. His hair is Brutus style, cropped close but with a short fringe in front, and his right hand is tucked in his waistcoat.
|}

If the same person or object appears in many images of an article, later images' alt text can assume that the reader has already read the first image's alt text and caption. For example, if in the ''[[Greta Garbo]]'' article the first image's  alt text describes Garbo's appearance in some detail, alt text for images later in the article can simply say "Garbo" instead of repeatedly describing her appearance. However, in other articles a typical Wikipedia reader cannot be expected to know what Garbo looked like, so an image of her should typically not have Garbo's name in its alt text.

{| class="wikitable"
|+ Assume context provided by earlier images when writing alt text for later images.
! Context !! Image !! Flawed alt text !! Better alt text
|-
| First image in ''[[Greta Garbo]]''
| [[Image:Greta Garbo 1925 by Genthe-retouched.jpg|thumb|upright|center|alt=Head and shoulders profile of a young woman with a haunted expression, one hand raised to just touch the base of her throat|Photo by [[Arnold Genthe]], 1925]]
| A beautiful woman with a sad expression
| Head and shoulders profile of a young woman with a haunted expression, one hand raised to just touch the base of her throat
|-
| Followup image in ''[[Greta Garbo]]''
| rowspan=2 | [[Imagem:Greta Garbo in 1950.jpg|thumb|center|alt=A veiled woman in dark coat and hat writes at a counter.|Filling out U.S. citizenship paperwork in 1950]]
| rowspan=2 | A veiled Greta Garbo in dark coat and hat writes at a counter.
| A veiled Garbo in dark coat and hat writes at a counter.
|-
| Image in the ''[[United States nationality law#Naturalization|Naturalization]]'' section of ''[[United States nationality law]]'', an article where Garbo is not otherwise mentioned
| A veiled woman in dark coat and hat writes at a counter.
|}

== Brevity ==

Alt text should be concise, so that it does not burden the visually impaired reader with unnecessary text. It should not summarize unimportant details. As it is not meant to be a unique identifier for an image, alt text typically does not supply enough information to characterize an image unambiguously. The best length for alt text depends on the image and its context. Although images of complex subjects may need long descriptions, alt text should be considerably shorter than a hundred words for all but the most detailed images. Another rule of thumb is that an image's alt text is probably too complicated if it takes more than five minutes to write.

{| class="wikitable"
|+ Omit needless words.
! Context !! Image !! Flawed alt text !! Better alt text
|-
| First image of ''[[Pavel Bure]]''
| [[Image:Pavel Bure in Canucks uniform.jpg|thumb|upright|center|alt=A hockey player on the ice before spectators. He wears a white jersey with a big "C", and his youthful face has a serious expression.|Bure with the [[Vancouver Canucks]] in [[1997–98 NHL season|1997–98]]]]
| An ice hockey player in his late twenties wears a jersey with red, blue and silver trim and a logo composed of a whale breaking out of a stylized "C". His jersey features a patch of a black letter "A" on the top right side, a patch of a stylized maple leaf with two hockey sticks on the top left side and the number 10 on his upper right arm. He also wears a white helmet and black hockey pants and holds a black and yellow hockey stick diagonally across his torso. He has an expression of deep and serious concentration on his face.
| A hockey player on the ice before spectators. He wears a white jersey with a big "C", and his youthful face has a serious expression.
|}

Some images and media files may benefit from full descriptions that are too long for alt text. Examples include detailed graphs and maps, complicated diagrams, and longer videos. For such a file it is good practice to put a longer description in the ''Summary'' section of the file's page, with a brief summary of this description in the alt text. For example, ''[[:Image:Pavel Bure in Canucks uniform.jpg]]'' contains a long description similar to the "Flawed alt text" shown in the previous example. [[MediaWiki]] does not support the HTML [[longdesc attribute]] that was designed for these longer alternative descriptions.

=== Repetition ===

Alt text should minimize any repetition of the caption or other nearby text. A screen reader will say both the alt text and the caption, and any repetition will not be helpful. An image's caption typically should focus on explaining or identifying the image, and say little about visual appearance, which is obvious to a sighted reader. Because alt text should focus ''only'' on the visual appearance, alt text and caption typically do not overlap. If the caption or other nearby text does describe a purely visual aspect of an image, that aspect should normally be omitted from the alt text.

{| class="wikitable"
|+ Do not repeat the caption.
! Context !! Image !! Flawed alt text !! Better alt text
|-
| First image of ''[[Hindenburg disaster]]''
| [[Imagem:Hindenburg burning.jpg|thumb|center|alt=The rear third of a large zeppelin burns violently in midair next to a skeletal tower, with a fireball larger than the zeppelin itself.|''Hindenburg'' a few seconds after catching fire.]]
| A few seconds after the fire started, a third of the Hindenburg was already engulfed in flames, with a fireball larger than the zeppelin itself.
| The rear third of a large zeppelin burns violently in midair next to a skeletal tower, with a fireball larger than the zeppelin itself.
|}

=== Placeholders ===

In an article that focuses heavily on an image, the caption or nearby text may already sufficiently describe an image's visual appearance; in such cases the image's alt text may be as simple as "See caption." or "See adjacent text."

{| class="wikitable"
|+ Use a placeholder if adjacent text already describes the image well.
! Context !! Image !! Flawed alt text !! Better alt text
|-
| First image of ''[[Mona Lisa]]''
| [[Imagem:Mona Lisa.jpg|frameless|upright|center|alt=See adjacent text.]]
| Monumental half-length portrait of a woman with an enigmatic expression. The portrait models forms subtly and employs atmospheric illusionism.
| See adjacent text.
|}

=== Phrases to avoid ===

For brevity, alt text should not mention the fact that it substitutes for an image, as this substitution is already obvious to the reader. For example, avoid phrases like "photograph of", "diagram illustrating", and "showing". Typically it is relatively unimportant whether an image is color or black and white, and that detail can be omitted as well.

Normally the image file itself is irrelevant to the article. Thus, alt text should not mention:

* the file name
* the file format
* the size of the file
* the dimensions of the file
* instructions on how to view a bigger version of the image

Like article text, alt text should [[Wikipedia:Avoid peacock terms|avoid peacock terms]] such as "awesome" and "beautiful".

{| class="wikitable"
|+ Avoid less-useful phrases and peacock terms.
! Context !! Image !! Flawed alt text !! Better alt text
|-
| First image of ''[[Autism therapies]]''
| [[Imagem:Opening a window to the autistic brain.jpg|thumb|center|alt=A young child points, in front of a woman who smiles and points in the same direction.|A three-year-old with autism points to fish in an aquarium, as part of an experiment on the effect of intensive shared-attention training on language development.]]
| Color photograph showing a side view of an awesome young child pointing. Behind the child an impressive and inspirational woman smiles and points in the same direction. This reduced version of "Opening a window to the autistic brain.jpg" is a JPEG image that is 150 pixels wide and 140 pixels high. Click here to see the image description page.
| A young child points, in front of a woman who smiles and points in the same direction.
|}

== Constraints ==

Some constraints on alt text are imposed by Wikipedia policies and guidelines on neutrality and verifiability.

=== Neutrality ===

Wikipedia articles use a [[Wikipedia:Neutral point of view|neutral point of view]], and one way to accomplish this in article text is to eliminate descriptive and interpretive language. However, this type of language is often ''exactly'' what a blind person needs in order to visualise or comprehend an image. Alt text should be descriptive as well as neutral, and it need not be dull and superficial to achieve these goals. A clear and vivid interpretation of the image serves the visually impaired reader better than a dry and colorless recital of surface detail.

{| class="wikitable"
|+ Don't just recite surface detail in an attempt to be "neutral".
! Context !! Image !! Flawed alt text !! Better alt text
|-
| The ''[[Vincent van Gogh#Letters|Letters]]'' section of ''[[Vincent van Gogh]]''. The article's lead portrait, a painting, has already established van Gogh's appearance as an adult artist with a red beard.
| [[Imagem:VincentVanGoghFoto.jpg|thumb|upright|120px|center|alt=Headshot photo of the artist as a cleanshaven young man. He has thick, ill-kempt, wavy hair, a high forehead, and deep-set eyes with a wary, watchful expression.|Vincent van Gogh, age 18, {{circa|1871–1872}}. This portrait was taken at the time when he was working at the branch of Goupil & Cie's gallery at The Hague.]]
| Black and white image of a man seen from the neck up wearing a coat and white-collared shirt. His hair is about 10 cm long. He looks over the viewer's left shoulder. One ear is visible.
| Headshot photo of the artist as a cleanshaven young man. He has thick, ill-kempt, wavy hair, a high forehead, and deep-set eyes with a wary, watchful expression.
|}

=== Verifiability ===

Alt text should be [[Wikipedia:Verifiability|verifiable]]. Typically, it should be verifiable by a non-expert reader who is looking only at the image, and should not need to be supported by a [[Wikipedia:Reliable sources|reliable source]]. Any claim likely to be challenged should be either removed, moved to the caption or other nearby text, or supported by a reliable source there. Since alt text cannot contain footnotes and cannot easily cite sources, any citations needed to support the alt text should be placed in the caption or other article text. As with all other parts of Wikipedia articles, [[Wikipedia:No original research|original research]] should be avoided when writing alt text.

As a corollary of verifiability, alt text should describe an image accurately and precisely. Carefully inspect an image when writing its alt text: do not mistake a blob or a scratch on the image for an object, and do not call an image a [[drawing]] if it is actually an [[engraving]] or a [[woodcut]]. If you are describing something you know little about, such as period hairstyles or clothing, it is often helpful to consult a Wikipedia article on the subject, or to ask for help on the article's talk page. This is particularly important for symbolic objects; for example, saying that an angel is giving a saint a "small branch" or "a bunch of leaves" is significantly less helpful than saying the angel is giving a "palm frond", as palm fronds have a special significance in that context.

{| class="wikitable"
|+ Describe the image accurately and precisely.
! Context !! Image !! Flawed alt text !! Better alt text
|-
| The ''[[Daylight saving time #Complexity|Complexity]]'' section of ''[[Daylight saving time]]''
| [[Image:Willett memorial.JPG|thumb|upright|center|alt=A standing stone in a grassy field surrounded by trees. The stone contains a vertical sundial whose shadow falls near 4 o'clock. It is inscribed "HORAS NON NUMERO NISI ÆSTIVAS" and "SUMMER TIME ACT 1925".|The [[William Willett]] Memorial Sundial is always on DST.]]
| A gravestone with a sundial that reads 12:30, sitting in somebody's yard. The sundial is about 4 meters high and contains some lettering in Italian. The stone is cracked near the bottom in two places.
| A standing stone in a grassy field surrounded by trees. The stone contains a vertical sundial centered on 1 o'clock, and is inscribed "HORAS NON NUMERO NISI ÆSTIVAS" and "SUMMER TIME ACT 1925".
|}
-->

== Limitações ==

O texto alt é limitado pelas restrições especificadas pela sintaxe Wiki e HTML, bem como as restrições de leitores de tela e outros navegadores.

=== Marcação ===

Textos alternativos não podem conter marcação wiki ou HTML. Por exemplo, o seguinte exto alternativo inválido:
<blockquote><code><nowiki>
[[circa|c.]] 1860 {{dic|saia-balão}} contendo 3 m<sup>2</sup> de tecido
</nowiki></code></blockquote>
Nem "<code><nowiki>[[circa|c.]]</nowiki></code>", nem "<code><nowiki>{{dic|saia-balão}}</nowiki></code>" ou "<code><nowiki><sup></nowiki></code>" tem o efeito esperado em textos substitutos.

=== Quebra de linhas ===

O texto alt deve estar apresentado em apenas uma linha, para evitar um bug [[MediaWiki]]. Em outras palavras, não adicione quebras de linhas no mesmo. Por exemplo

  <pre>  <!-- Isto não funciona. -->
  [[Imagem:Example.png|20x20px|alt=Imagem
  de exemplo]]</pre>

gerará uma imagem "[[Imagem:Example.png|20x20px|alt=Imagem
de exemplo]]" cujo texto alternativo e título seriam ambos "alt=Imagem de exemplo". Aparentemente "<code>alt=''XXX''</code>" é tratada incorretamente como legenda quando <code>''XXX''</code> contém quebras de linhas.

<!--
=== Text ===

When an image focuses on text, its alt text should normally contain that text as accurately as is feasible, even if the text contains unusual characters. This benefits people whose screen readers can handle the text. Some screen readers cannot handle obscure [[Unicode]] characters, and either render them as "?" or ignore them entirely; therefore, when it is easy, word the alt text so that it makes some sense even if the unusual characters are ignored or read aloud as "?". In alt text for these images, omit details such as color or font unless the images focus on or illustrate these details.

{| class="wikitable"
|+ Transcribe the image's text, even if it has unusual characters.
! Context !! Image !! Flawed alt text !! Better alt text
|-
| First image of ''[[Yuan (surname)]]''
| [[Image:Yuan character (1st century).png|thumb|upright=0.55|center|alt=The character "袁"|The character "Yuan", in small seal style, adapted from the 2nd century [[Yuan An]] stele]]
| A character written in red on a white background
| The character "袁"
|-
| The ''[[Hindi#Writing system|Writing system]]'' section of ''[[Hindi]]''
| [[Imagem:Hindi.svg|thumb|upright=0.55|center|alt=The word हिन्दी|One way to write the word "Hindi" in Devanagari]]
| SVG image of a rendering for "Hindi" in Devanagari
| The word हिन्दी
|-
| The ''[[Otomi language#Orthography|Orthography]]'' section of ''[[Otomi language]]''
| [[Imagem:Bienvenidos a Ixmiquilpan.jpg|thumb|upright=1.2|center|Sign written in Otomi and Spanish in the Mezquital Valley|alt=A large overhead road sign says "BIENVENIDOS A IXMIQUILPAN", then (smaller) "HOGÄ EHE NTS'U&#818;TK'ANI", then (larger again) "CORAZON DEL VALLE DEL MEZQUITAL".]]
| Picture of a large blue sign saying "Bienvenidos a ixmiquilpan: Corazon del Valle de Mezquital" and in smaller letters "hogä ehe nts'utk'ani". Behind the sign are rolling green hills.
| A large overhead road sign says "BIENVENIDOS A IXMIQUILPAN", then (smaller) "HOGÄ EHE NTS'U&#818;TK'ANI", then (larger again) "CORAZON DEL VALLE DEL MEZQUITAL".
|}

Normally alt text should avoid tricky typographical constructions that are likely to confuse screen readers. [[ASCII]] constructions like "1/2" are typically read aloud as "1 slash 2" rather than as the more helpful "one half". Abbreviations like "m" for "meter" are less helpful when read aloud, and are often best avoided. The [[non-breaking space]] "<code><nowiki>&amp;nbsp;</nowiki></code>" does not affect alt text layout behavior as it does with article text, and should be avoided to simplify editing.

{| class="wikitable"
|+ Avoid unnecessarily tricky lettering.
! Context !! Image !! Flawed alt text !! Better alt text
|-
| The ''[[Stairway#Gallery|Gallery]]'' section of ''[[Stairway]]''
| [[Image:VaticanMuseumStaircase.jpg|thumb|120px|center|alt=Vast spiral staircase, half in darkness. It is a stepped ramp about 15 meters in diameter, and descends 5 stories at about a 10 degree incline.|[[Spiral]] ([[double helix]]) stairs of the [[Vatican Museums]]]]
| Vast ꩜ ▁▂▃▄▅▆▇█, 1/2 in darkness. It is a stepped ramp about 15&amp;nbsp;m in diameter, and descends 5 stories at about a 10° incline.
| Vast spiral staircase, half in darkness. It is a stepped ramp about 15 meters in diameter, and descends 5 stories at about a 10 degree incline.
|}

Too-tiny or otherwise-illegible text need not be transcribed. The image's file page can transcribe text that can be read only by viewing the full-size image, or the file page can link to a transcription.

{| class="wikitable"
|+ Illegible text need not be transcribed.
! Context !! Image !! Flawed alt text !! Better alt text
|-
| The ''[[Dick Turpin#Modern view|Modern view]]'' section of ''[[Dick Turpin]]''
| [[Imagem:Dick Turpin Richard Bayes.djvu|thumb|upright|center|alt=Title page of a book, headed "The Genuine HISTORY of the LIFE of RICHARD TURPIN"|Richard Bayes' account is the source of several of the modern myths surrounding Dick Turpin.]]
| Title page of a book, saying "The Genuine HISTORY of the LIFE of RICHARD TURPIN, The noted Highwayman, Who was Executed at York for Horse-stealing, under the Name of John Palmer, on Saturday April, 7, 1739. I. A True Narrative of his Transactions from his Birth to his Marriage and settling at Suson as a Butcher. II. An Account of his being a Smuggler in the Hundreds of Essex; his turning Dear-Strealer; his Exploits with Gregory, Fielder, Rose, Wheeler, and the rest of the Essex Gang. III. His breaking from that Gang, and an humourous Adventure, by Means of which he got acquainted with King. IV. Of his being pursued in White-chaple by Mr. Bayes, where he shot his Companion King by Mistake. V.... VI.... VII.... VIII.... IX.... The Whole collected from well attested Facts, and communicated by Mr. Richard Bayes, at the Green-Man on Epping-Forest, and other Persons of that County. LONDON: Printed for J. Standen, at D'&nbsp;Anvers's Head oppoſite Serjeants-Inn in Chancery-Lane."
| Title page of a book, headed "The Genuine HISTORY of the LIFE of RICHARD TURPIN"
|}

== Quando especificar ==

Por questões de [[Wikipedia:Acessibilidade|acessibilidade]], toda imagem dever ter um ter um texto alt should lack a link. An image normally needs alt text so that a visually impaired reader knows what the image looks like or what will happen when the image is clicked. In the typical case, where a Wikipedia image is a <code>[[Wikipedia:Picture tutorial#thumb|thumb]]</code> or <code>[[Wikipedia:Picture tutorial#frame|frame]]</code> that links to the image's page, some alternative text should be specified. Otherwise, the alt text would be empty and a screen reader normally would say the file name, which is usually not helpful.<ref>{{citar web|url=http://www.w3.org/TR/2008/NOTE-WCAG20-TECHS-20081211/F89 |título=F89: Failure of 2.4.4, 2.4.9 and 4.1.2 due to using null alt on an image where the image is the only content in a link}} In {{Harvnb|WAI|2008b}}.</ref>

=== Defaulting to caption ===

A [[Wikipedia:Picture tutorial #Plain pictures|plain picture]] (''i.e.'', not a <code>thumb</code> or <code>frame</code>) can omit the "{{para|alt}}" parameter when its caption is brief and adequate for alt text. For such images, the alt text defaults to the caption instead of being empty. For example, <code><nowiki>[[Imagem:Checkmark green.svg|24x24px |Green checkmark]]</nowiki></code> generates an image [[Imagem:Checkmark green.svg|24x24px |Green checkmark]] with alt text and title both set to "Green checkmark". In a plain picture that has no caption, the default alt text is the image's file name; this default is usually not helpful, and alt text should be specified explicitly.

=== Links ===
{{see also|Wikipedia:Images linking to articles}}
Some non-<code>thumb</code> images use the "<code>[[Wikipedia:Picture tutorial#link|link]]=''Page''</code>" parameter to cause the image to link to <code>''Page''</code> rather than to the image page. The alt text for these images should briefly describe the function of the image, not its visual appearance. This is commonly combined with alt text defaulting to the caption, as described in the previous section. For example:

[[Imagem:Commons-logo.svg|frameless |upright=0.3 |border |left |link=Commons:Special:Search |Search Wikimedia Commons]]
<blockquote><code><nowiki>
[[Imagem:Commons-logo.svg|frameless |upright=0.3 |border |left |link=Commons:Special:Search |Search Wikimedia Commons]]
</nowiki></code></blockquote>
{{-}}

=== Image maps ===

<imagemap>
Image:Bryan-Sewall.jpg|300px|right|alt=1896 Democratic campaign poster with nominees William J. Bryan of Nebraska for President and Arthur Sewall of Maine for Vice President
circle 950 850 700 [[William Jennings Bryan|William J. Bryan]]
circle 2950 850 700 [[Arthur Sewall]]
default [http://projects.vassar.edu/1896/democrats.html 1896 Democrats]
</imagemap>
In an [[mw:Extension:ImageMap|image map]], where different parts of an image link to different locations, the markup's first line specifies the base image's alt text, which should describe the image's visual appearance; each subsequent line specifies the alt text for a region, which should describe what happens when you click on that region. For example, the image at right is generated by the following markup:

<pre style="overflow:auto;">
<imagemap>
Image:Bryan-Sewall.jpg|300px|right|alt=1896 Democratic campaign poster with nominees William J. Bryan of Nebraska for President and Arthur Sewall of Maine for Vice President
circle 950 850 700 [[William Jennings Bryan|William J. Bryan]]
circle 2950 850 700 [[Arthur Sewall]]
default [http://projects.vassar.edu/1896/democrats.html 1896 Democrats]
</imagemap>
</pre>

This markup's first line says that the base image's alt text is "1896 Democratic campaign poster with nominees William J. Bryan of Nebraska for President and Arthur Sewall of Maine for Vice President". Later lines say that the alt text is "William J. Bryan" for the left portait region, "Arthur Sewall" for the right portrait region, and "1896 Democrats" for the remaining region.
-->
=== Imagens puramente decorativas ===
{| class="wikitable" style="float:right; margin:0 0 0 0.5em;"
|+ Uma tabela com imagens puramente decorativas
|-
! Posição
! Nome
! País
|-
| align=center | 1
| [[Shizuka Arakawa]]
| {{flagIOC|JPN|Inverno de 2006}}
|-
| align=center | 2
| [[Sasha Cohen]]
| {{flagIOC|USA|Inverno de 2006}}
|-
| align=center | 3
| [[Irina Slutskaya]]
| {{flagIOC|RUS|Inverno de 2006}}
|-
| align=center | 4
| [[Fumie Suguri]]
| {{flagIOC|JPN|Inverno de 2006}}
|-
| align=center | 5
| [[Joannie Rochette]]
| {{flagIOC|CAN|Inverno de 2006}}
|}

Uma imagem ''puramente decorativa'' é aquela que não tem função de transmitir nenhuma informação adicional útil porque é utilizada apenas para formatação visual ou decoração. Por exemplo, na tabela de [[Patinação_artística_nos_Jogos_Olímpicos_de_Inverno_de_2006_-_Individual_feminino#Resultados_finais|patinação artística nas Olimpíadas de 2006]] a direita, cada imagem de bandeira é puramente decorativa, porque não transmite nenhuma informação que não esteja informada pelo texto adjacente, como o nome dos países. Nada acontece ao clicar sobre a imagem.

Na marcação wiki, apenas imagem sem borda podem ser puramente decorativas; uma imagem "thumb" (miniatura) não pode ser simplesmente decorativa, pois a mesma possui uma função: algo acontece quando você clica nela.

Uma imagem puramente decorativa não deve ter ligação para outra página ou texto alt, de modo que os leitores de tela possam ingorá-las. Ícones e imagens sem ligações não devem texto alternativo se a imagem for puramente decorativa.<ref>{{citar web|url=http://www.w3.org/TR/2008/NOTE-WCAG20-TECHS-20081211/H67 |título=H67: Using null alt text and no title attribute on img elements for images that AT should ignore }} In {{Harvnb|WAI|2008b}}.</ref>

Use "<code><nowiki>[[Imagem: ... |ligação=|alt=]]</nowiki></code>" para desabilitar o texto alternativo que seria gerado normalmente para a imagem. Por exemplo, <code><nowiki>[[Imagem:Checkmark green.svg|24x24px |link= |alt=]]</nowiki></code> gera uma imagem [[Imagem:Checkmark green.svg|24x24px |link= |alt=]] sem texto alternativo e sem ligação a outra página. Remover a ligação dessas imagens melhor a [[usuabilidade web]], pois ter uma ligação poderia confundir o leitor.

<!--
== Appearance ==

Here is an example [[WP:PIC#thumb|thumb]] image with alt text, and how it might appear to various browsers. The context is the lead infobox of ''[[Philitas of Cos]]''.

; Wikipedia code
:: <small>''(The following example may be folded into multiple lines to keep it on the page, but the actual text should be all on one line.)''</small>
<blockquote><code><nowiki>
[[Image:Antikythera philosopher.JPG |thumb |upright |left |alt=Bronze head of bearded man with furrowed brow and unruly hair |The ''Philosopher'' ({{circa|250–200 BC|lk=abbr}}) from the [[Antikythera wreck]] illustrates the style used by Hecataeus in his bronze of Philitas.]]
</nowiki></code></blockquote>

The phrase "Bronze head of bearded man with furrowed brow and unruly hair" is the text that will be rendered in place of the image.

; Result in a screen reader

A [[screen reader]] might say the following words (the alt text is underlined):
:"link <ins>bronze head of bearded man with furrowed brow and unruly hair</ins> the philosopher cee 250 dash 200 bee cee from the link Antikythera wreck illustrates the style used by Hecataeus in his bronze of Philitas"
Without the alt text, the same screen reader might say the following, which is less useful:
:"link <ins>file colon Antikythera underscore philosopher dot jay pee gee</ins> the philosopher cee 250 dash 200 bee cee from the link Antikythera wreck illustrates the style used by Hecataeus in his bronze of Philitas"

; Result in your browser
[[Image:Antikythera philosopher.JPG |thumb |upright |left |alt=Bronze head of bearded man with furrowed brow and unruly hair |The ''Philosopher'' ({{circa|250–200 BC|lk=abbr}}) from the [[Antikythera wreck]] illustrates the style used by Hecataeus in his bronze of Philitas.]]

This shows how the image is displayed in your browser.
{{-}}

; With images disabled
<div class="thumb tleft">
<div class="thumbinner" style="width:140px;">[[:Image:Antikythera philosopher.JPG|<ins>Bronze head of bearded man with furrowed brow and unruly hair</ins>]]
<div class="thumbcaption">
The ''Philosopher'' ({{circa|250–200 BC}}) from the [[Antikythera wreck]] illustrates the style used by Hecataeus in his bronze of Philitas.
</div>
</div>
</div>

This shows what might be displayed in a web browser with images turned off. Many modern browsers allow users to turn off images (for example, if they are using a low-bandwidth connection). The alt text is often rendered in place of the image. Here, the phrase serves as a useful replacement for the image.
{{-}}

Instead of a caption, a [[WP:PIC#Plain pictures|plain picture]] has a title attribute, which is computed by removing Wiki markup from the text that would ordinarily be the caption. If you hover over a plain picture with your mouse, many browsers display a [[tooltip]] containing the image's title attribute. For example:

; Wikipedia code
:: <small>''(The following example may be folded into multiple lines to keep it on the page, but the actual text should be all on one line.)''</small>
<blockquote><code><nowiki>
[[Image:Tizian 117.jpg |140px |right |alt=Half-length portrait painting of a richly dressed young woman |[[Titian]]'s daughter Lavinia, {{c.|1545}}]]
</nowiki></code></blockquote>

; Result in a screen reader
:"link Half-length portrait painting of a richly dressed young woman"

; Result in your browser
[[Image:Tizian 117.jpg |140px |right |alt=Half-length portrait painting of a richly dressed young woman |[[Titian]]'s daughter Lavinia, {{c.|1545}}]]

This shows how the image is displayed in your browser. Mouse over it to see the title attribute; this attribute is simply "Titian's daughter Lavinia, c. 1545", as the square brackets in the Wiki markup "<code><nowiki>[[Titian]]</nowiki></code>" have no effect, and the fancy formatting generated by the {{tl|c.}} template is rendered simply as a space. [[Internet Explorer 7]] and earlier versions display alt text instead of title text when you hover; this bug was fixed in [[Internet Explorer 8]].
{{-}}

; With images disabled
<div class="floatright">[[:File:Tizian_117.jpg|<span title="Titian's daughter Lavinia, c. 1545">Half-length portrait painting of a richly dressed young woman</span>]]</div>

This shows what might be displayed in a web browser with images turned off. Again, the title attribute lacks the italics or wikilink of the markup.

== Writing the text ==

Often the best person to write alt text for an image is the person who added the image to the article, and who presumably knows the image's context. When adding an image, take a couple of minutes to describe it in the context of its caption and adjacent text. It can be helpful to read the text aloud in the order it appears in the Wiki markup (with alt text before caption), to catch unwanted repetition and awkward transitions. You can also disable images in your browser to see the alt text in place before you save it.

Check the article with the [[tools:~dispenser/cgi-bin/altviewer.py|Altviewer tool]], a [[m:Toolserver|Wikimedia Toolserver]] tool that displays all the images in a Wikipedia page, next to their alt text. Look for alt text that is missing or cryptic or too long, and for alt text that is a near-duplicate of the caption. At times the Altviewer's results are delayed, so it may help to check an article a day after editing it heavily.

If an image is generated by a template, you may need to change the template to cause it to generate proper alt text. The simplest case is a template like {{tl|Infobox}}, which has parameters like "<code><nowiki>image=[[Imagem:Example.png|alt=Example alt text]]</nowiki></code>" where the template's invoker specifies the alt text as part of a parameter value, which means that the template already supports alt text and does not need to be changed. A common template change is to add support for an "<code>alt=</code>" parameter to the template for each parameter that names images, as was {{diff|Template:Infobox officeholder|302544867|300095526|done}} for the {{tl|Infobox officeholder}} template. Another common template change is to add "<code>|link=|alt=</code>" to purely decorative images generated by the template, as was {{diff|Template:Sky|309484988|307784954|done}} for the {{tl|Sky}} template. Occasionally a template may need to have parameters for both alt text and link, so that the invoker can specify whether an image is purely decorative, as was {{diff|Template:Portal|303450656|278218734|done}} for the {{tl|Portal}} template. If the template is protected you may need to edit its sandbox and then request via {{tl|editprotected}} that the change be installed.

If you're still unsure about the best alternative text for an image, or how to change a template, please leave a note on [[Wikipedia talk:Alternative text for images|this article's talk page]], and someone will help you out.
-->
== História ==

Até 2008, o texto alternativo da imagem era automaticamente o mesmo da legenda, que resultava em duas desvantagens. Primeiro, isso significa que à imagem da legenda era lida duas vezes pelo leitor de tela, uma para o texto alt e outra para a legenda em si. Segundo, legendas nem sempre descrevem suas imagens, mas sim seu significado para o leitor.

Um novo sistema foi introduzido em outubro de 2008.<ref>"[[rev:41837|Allow <code>alt=</code> attribute for images]]" (2008-10-08). MediaWiki r41837 – code review.</ref> Ele permite que os wikipedistas especifiquem o texto alt independentemente da legenda. A legenda é um parâmetro não nomeado na sintaxe, tal como antes; já o texto alternativo é especificado pelo parâmetro "<code>alt=</code>". Neste novo sistema, o texto alt serve para ''descrever'' a imagem a aqueles que não podem ver, enquanto a legenda transmite a informação essencial além do que pode ser visto.

O [[bugzilla:19906|bug Wikimedia 19906]] propõe que o texto padrão alternativo para uma imagem esteja em sua própria página de imagem, para simplificar o trabalho de especificar o texto alt para a mesma imagens em vários artigos.

== Ver também ==
* [[tools:~dispenser/cgi-bin/altviewer.py|Altviewer tool]] – Verifica o texto alternativo em uma página wiki

== Notas ==
{{reflist}}

== Referências ==
* {{citar web |url=http://www.w3.org/TR/WCAG20/ |título=Web Content Accessibility Guidelines (WCAG) 2.0 |data=2008-12-11 |acessodata=2009-07-06 |publicado=W3C Web Accessibility Initiative |autor=Caldwell B, Cooper M, Guarino Reid L ''et al.'' (eds.) |ref=CITEREFWAI2008a}}
* {{citar web |url=http://www.w3.org/TR/WCAG20-TECHS/ |título= Techniques for WCAG 2.0 |data=2008-12-11 |acessodata=2009-07-06 |publicado=W3C Web Accessibility Initiative |autor=Caldwell B, Cooper M, Guarino Reid L ''et al.'' (eds.) |ref=CITEREFWAI2008b }}

[[Categoria:!Acessibilidade]]