Proposed HTML images contain no text
Description
This rule checks that images of text are not used
Applicability
This rule applies to any image resources rendered in a web page.
Expectation
Each test target has no visible text, except if at least one of the following is true:
- decorative: The image with text is purely decorative; or
- incidental: The text is not a significant part of the image; or
- essential: Ensuring presentation of the text is essential.
Assumptions
- There is no mechanism to change the rendered text in the image resource. Otherwise, the rule might fail while SC 1.4.5 Images of Text and SC 1.4.9 Images of Text (No Exception) might be satisfied.
- The specific presentation of the text rendered in the image resource can be achieved through formatted text. Otherwise, the rule might fail while SC 1.4.5 Images of Text and SC 1.4.9 Images of Text (No Exception) might be satisfied.
- When used in HTML, the SVG
<text>
element is not considered to be an image of text. This is because like any other element in HTML, SVG<text>
can be adjusted through custom style sheets. This does not apply for SVG text that is in a separate file, and displayed through, for example, theimg
element.
Accessibility Support
There are no accessibility support issues known.
Background
This rule is designed specifically for SC 1.4.5 Images of Text which includes exceptions to the images it applies to that are not part of SC 1.4.9 Images of Text (No Exception). Therefore, some images that are inapplicable for this rule can be applicable to SC 1.4.9 Images of Text (No Exception).
Bibliography
- Understanding Success Criterion 1.4.5: Images of Text
- Understanding Success Criterion 1.4.9: Images of Text (No Exception)
Accessibility Requirements Mapping
1.4.5 Images of Text (Level AA)
- Learn more about 1.4.5 Images of Text
- Required for conformance to WCAG 2.0 and later on level AA and higher.
- Outcome mapping:
- Any
failed
outcomes: success criterion is not satisfied - All
passed
outcomes: success criterion needs further testing - An
inapplicable
outcome: success criterion needs further testing
- Any
1.4.9 Images of Text (No Exception) (Level AAA)
- Learn more about 1.4.9 Images of Text (No Exception)
- Required for conformance to WCAG 2.0 and later on level AAA.
- Outcome mapping:
- Any
failed
outcomes: success criterion is not satisfied - All
passed
outcomes: success criterion needs further testing - An
inapplicable
outcome: success criterion needs further testing
- Any
Input Aspects
The following aspects are required in using this rule.
Test Cases
Passed
Passed Example 1
This image resource referenced by the img
element does not contain text.
<img src="/test-assets/shared/fireworks.jpg" alt="fireworks going off behind the Eiffel tower at night" />
Passed Example 2
This image resource referenced by the input
element does not contain text.
<input type="image" src="/test-assets/shared/file.svg" alt="New file" />
Passed Example 3
This image resource referenced by the svg
element does not contain text.
<svg width="2in" height="3in" xmlns="http://www.w3.org/2000/svg">
<image x="20" y="20" width="200px" height="100px" href="/test-assets/shared/fireworks.jpg">
<title>Fireworks in Paris</title>
</image>
</svg>
Passed Example 4
This image resource referenced by the object
element contains text, but it is not the most significant content.
<object data="/test-assets/0va7u6/times_square.jpg" title="Picture of Times Square, New York"></object>
Passed Example 5
This image resource referenced by the img
element contains text, but its presentation is essential to convey the information.
<p>
The following image is a close up of the cover of a Classic Comics book titled "Ivanhoe" illustrating a font that
looks like an old Gothic style font.
</p>
<img
src="/test-assets/0va7u6/ivanhoe.png"
alt="The word Ivanhoe written in a style that resembles old medieval letters. The letter I is colored to resemble copper. The remaining letters are black. The background is yellow."
/>
Passed Example 6
This image resource referenced by the background-image
property of the div
element contains a logo with text. Logotypes are considered an essential exception.
<div
role="img"
aria-label="W3C logo"
style="
width: 100px;
height: 100px;
background-image: url(/test-assets/shared/w3c-logo.png);
background-repeat: no-repeat;
"
></div>
Passed Example 7
This image resource referenced by the img
element is an image of text (the book covers), but it is just meant to decorate the webpage of a book store, therefore it is decorative.
<img src="/test-assets/0va7u6/books.jpg" alt="" />
<p>Welcome to my book store</p>
Passed Example 8
These image resources referenced by the input
elements are images of text (the letter “A”), but they are not expressing anything in a human language. The image is only used to indicate how the font size can be controlled.
<input
type="image"
src="/test-assets/0va7u6/smallA.png"
style="border: 1px solid black;"
width="50px"
height="50px"
alt="Decrease text size"
/>
<input
type="image"
src="/test-assets/0va7u6/bigA.png"
style="border: 1px solid black;"
width="50px"
height="50px"
alt="Increase text size"
/>
Failed
Failed Example 1
This image resource referenced by the img
element contains text for which the particular presentation is not essential.
<img
src="/test-assets/0va7u6/textimage.jpg"
alt="The Accessibility Conformance Testing (ACT) Rules Format 1.0 defines a format for writing accessibility test rules."
/>
Failed Example 2
This image resource referenced by the input
element in the Image Button contains text for which the particular presentation is not essential.
<input type="image" src="/test-assets/0va7u6/button.jpg" alt="Press me" />
Failed Example 3
This image resource referenced by the background-image
property of the div
element contains text for which the particular presentation is not essential.
<div style="background-image: url(/test-assets/0va7u6/textimage.jpg); width: 500px; height: 200px;" />
Failed Example 4
This image resource referenced by the img
element contains text that provides redundant information, but it still is information, therefore it is not decorative.
<img src="/test-assets/0va7u6/welcome.png" alt="" />
<p>Welcome to our website</p>
Failed Example 5
This img
element loads an SVG with text as an image resource. Because the SVG is loaded as an image resource, instead of being embedded in HTML the text cannot be selected or customized.
<img alt="WCAG Rocks" src="data:image/svg+xml;utf8,
<svg xmlns='http://www.w3.org/2000/svg' height='20px' width='80px'>
<text x='0' y='15'>WCAG Rocks</text>
</svg>" />
Inapplicable
Inapplicable Example 1
The resource referenced by the object
element does not have visible pixels.
<object date="/test-assets/0va7u6/textimage.jpg" style="display: none"></object>
Inapplicable Example 2
This svg
element does not have image
element descendants.
<svg xmlns="http://www.w3.org/2000/svg">
<text x="20" y="35">My</text>
<text x="45" y="35">cat</text>
<text x="55" y="55">is</text>
<text x="70" y="55">Grumpy!</text>
</svg>
Glossary
Attribute value
The attribute value of a content attribute set on an HTML element is the value that the attribute gets after being parsed and computed according to specifications. It may differ from the value that is actually written in the HTML code due to trimming whitespace or non-digits characters, default values, or case-insensitivity.
Some notable case of attribute value, among others:
- For enumerated attributes, the attribute value is either the state of the attribute, or the keyword that maps to it; even for the default states. Thus
<input type="image" />
has an attribute value of eitherImage Button
(the state) orimage
(the keyword mapping to it), both formulations having the same meaning; similarly, “an input element with atype
attribute value ofText
” can be either<input type="text" />
,<input />
(missing value default), or<input type="invalid" />
(invalid value default). - For boolean attributes, the attribute value is
true
when the attribute is present andfalse
otherwise. Thus<button disabled>
,<button disabled="disabled">
and<button disabled="">
all have adisabled
attribute value oftrue
. - For attributes whose value is used in a case-insensitive context, the attribute value is the lowercase version of the value written in the HTML code.
- For attributes that accept numbers, the attribute value is the result of parsing the value written in the HTML code according to the rules for parsing this kind of number.
- For attributes that accept sets of tokens, whether space separated or comma separated, the attribute value is the set of tokens obtained after parsing the set and, depending on the case, converting its items to lowercase (if the set is used in a case-insensitive context).
- For
aria-*
attributes, the attribute value is computed as indicated in the WAI-ARIA specification and the HTML Accessibility API Mappings.
This list is not exhaustive, and only serves as an illustration for some of the most common cases.
The attribute value of an IDL attribute is the value returned on getting it. Note that when an IDL attribute reflects a content attribute, they have the same attribute value.
Embedded Image
An element presents an embedded image when any of the following is true:
- the element is an
img
element with a non-empty source set; or - the element is an
input
element with atype
attribute value ofimage
and itssrc
attribute value is not empty; or - the element is an
object
element with adata
attribute value referencing a resource with an image MIME type; or - the element is an
svg
element having one or moreimage
descendants with a non-emptyhref
attribute value; or - the element has a computed
background-image
CSS property with at least oneimage
that is a url reference.
Essential text presentation
The presentation of text is considered essential in one of more of the following scenarios:
- The text and its presentation is part of a brand; or
- The text is part of a digitized image of a physical object; or
- The text is part of a free-form digital illustration; or
- The text is part of an image with other graphical objects, where its relationship is informative; or
- Changing part of the presentation would alter the meaning of content on the page.
Examples of text for which the presentation is essential include:
- Logos, product names, or slogans
- Image of a hand-written letter, picture of a street sign, or a scanned contract
- A digital signature, or a note written using a stylus,
- A bar chart, diagram, or maps with place names
- An image showing a font, or showing the difference between font-weights
Note: WCAG includes a generic definition of “essential”.
Insignificant
Content that is neither purely decorative, nor required for understanding the purpose of certain pieces of information or functionality. Insignificant content is often used to provide context.
Example: A picture of New York’s Time Square may include taxis, a famous pizza restaurant, and theater advertisements, etc. None of these are purely decorative. They provide clues as to where the picture was taken. But neither are any of these required to understand the picture as a whole. Even if the picture itself is significant, the taxis in the picture are not.
Outcome
An outcome is a conclusion that comes from evaluating an ACT Rule on a test subject or one of its constituent test target. An outcome can be one of the three following types:
- Inapplicable: No part of the test subject matches the applicability
- Passed: A test target meets all expectations
- Failed: A test target does not meet all expectations
Note: A rule has one passed
or failed
outcome for every test target. When there are no test targets the rule has one inapplicable
outcome. This means that each test subject will have one or more outcomes.
Note: Implementations using the EARL10-Schema can express the outcome with the outcome property. In addition to passed
, failed
and inapplicable
, EARL 1.0 also defined an incomplete
outcome. While this cannot be the outcome of an ACT Rule when applied in its entirety, it often happens that rules are only partially evaluated. For example, when applicability was automated, but the expectations have to be evaluated manually. Such “interim” results can be expressed with the incomplete
outcome.
Rendered Image Resource
A rendered image resource in a web page is any resource with visible pixels that has been specified in the list of image sources of an embedded image.
Visible
Content perceivable through sight.
Content is considered visible if making it fully transparent would result in a difference in the pixels rendered for any part of the document that is currently within the viewport or can be brought into the viewport via scrolling.
For more details, see examples of visible.
Web page (HTML)
An HTML web page is the set of all fully active documents which share the same top-level browsing context.
Note: Nesting of browsing context mostly happens with iframe
and object
. Thus a web page will most of the time be a “top-level” document and all its iframe
and object
(recursively).
Note: Web pages as defined by WCAG are not restricted to the HTML technology but can also include, e.g., PDF or DOCX documents.
Note: Although web pages as defined here are sets of documents (and do not contain other kind of nodes), one can abusively write that any node is “in a web page” if it is a shadow-including descendant of a document that is part of that web page.
Rule Versions
This is the first version of this ACT rule.
Implementations
This section is not part of the official rule. It is populated dynamically and not accounted for in the change history or the last modified date.