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Proposed Image accessible name is descriptive

Description

This rule checks that the accessible names of images serve an equivalent purpose to the image.

Applicability

This rule applies to any img, canvas or svg element that is visible and has a non-empty accessible name, except if one or more of the following is true:

Expectation

Each test target has an accessible name that serves an equivalent purpose to the non-text content of that test target.

Assumptions

There are no assumptions.

Accessibility Support

Some popular browser / screen reader combinations do not pronounce the accessible names of svg elements. This can be resolved by adding an explicit semantic role of img to the svg element.

Background

Bibliography

Accessibility Requirements Mapping

Input Aspects

The following aspects are required in using this rule.

Test Cases

Passed

Passed Example 1

Open in a new tab

This img element has an alt attribute that describes the image.

<html lang="en">
	<img src="/test-assets/shared/w3c-logo.png" alt="W3C logo" />
</html>

Passed Example 2

Open in a new tab

This svg element has an aria-label attribute that describes the HTML5 logo image.

<html lang="en">
	<svg viewBox="0 0 512 512" aria-label="HTML 5 logo" role="img">
		<path
			d="M108.4 0h23v22.8h21.2V0h23v69h-23V46h-21v23h-23.2M206 23h-20.3V0h63.7v23H229v46h-23M259.5 0h24.1l14.8 24.3L313.2 0h24.1v69h-23V34.8l-16.1 24.8l-16.1-24.8v34.2h-22.6M348.7 0h23v46.2h32.6V69h-55.6"
		/>
		<path fill="#e44d26" d="M107.6 471l-33-370.4h362.8l-33 370.2L255.7 512" />
		<path fill="#f16529" d="M256 480.5V131H404.3L376 447" />
		<path
			fill="#ebebeb"
			d="M142 176.3h114v45.4h-64.2l4.2 46.5h60v45.3H154.4M156.4 336.3H202l3.2 36.3 50.8 13.6v47.4l-93.2-26"
		/>
		<path fill="#fff" d="M369.6 176.3H255.8v45.4h109.6M361.3 268.2H255.8v45.4h56l-5.3 59-50.7 13.6v47.2l93-25.8" />
	</svg>
</html>

Passed Example 3

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This canvas element has an aria-label attribute that describes the W3C logo image.

<html lang="en">
	<canvas id="logo" width="72" height="48" aria-label="W3C logo"></canvas>
	<script>
		const img = new Image()
		img.src = '/test-assets/shared/w3c-logo.png'
		img.onload = function() {
			const ctx = document.querySelector('#logo').getContext('2d')
			ctx.drawImage(img, 0, 0)
		}
	</script>
</html>

Failed

Failed Example 1

Open in a new tab

This img element has an alt attribute that incorrectly describes the image.

<html lang="en">
	<img src="/test-assets/shared/w3c-logo.png" alt="ERCIM logo" />
</html>

Failed Example 2

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This svg element has an aria-label attribute that incorrectly describes the image (the aria-label is “W3C” but the actual image is the HTML5 logo).

<html lang="en">
	<svg viewBox="0 0 512 512" aria-label="W3C" role="img">
		<path
			d="M108.4 0h23v22.8h21.2V0h23v69h-23V46h-21v23h-23.2M206 23h-20.3V0h63.7v23H229v46h-23M259.5 0h24.1l14.8 24.3L313.2 0h24.1v69h-23V34.8l-16.1 24.8l-16.1-24.8v34.2h-22.6M348.7 0h23v46.2h32.6V69h-55.6"
		/>
		<path fill="#e44d26" d="M107.6 471l-33-370.4h362.8l-33 370.2L255.7 512" />
		<path fill="#f16529" d="M256 480.5V131H404.3L376 447" />
		<path
			fill="#ebebeb"
			d="M142 176.3h114v45.4h-64.2l4.2 46.5h60v45.3H154.4M156.4 336.3H202l3.2 36.3 50.8 13.6v47.4l-93.2-26"
		/>
		<path fill="#fff" d="M369.6 176.3H255.8v45.4h109.6M361.3 268.2H255.8v45.4h56l-5.3 59-50.7 13.6v47.2l93-25.8" />
	</svg>
</html>

Failed Example 3

Open in a new tab

This canvas element has an aria-label attribute that incorrectly describes the image (the aria-label is “HTML5 logo” but the actual image is the W3C logo).

<html lang="en">
	<canvas id="logo" width="72" height="48" aria-label="HTML 5 logo"></canvas>
	<script>
		const img = new Image()
		img.src = '/test-assets/shared/w3c-logo.png'
		img.onload = function() {
			const ctx = document.querySelector('#logo').getContext('2d')
			ctx.drawImage(img, 0, 0)
		}
	</script>
</html>

Inapplicable

Inapplicable Example 1

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This img element has an empty ("") accessible name. The image is described by the adjacent text.

<img src="/test-assets/shared/pdf-icon.png" alt="" /> PDF document

Inapplicable Example 2

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This decorative img element has an empty ("") accessible name because it has no attributes or content to provide an accessible name.

<html lang="en">
	<p>Happy new year!</p>
	<img src="/test-assets/shared/fireworks.jpg" role="presentation" />
</html>

Inapplicable Example 3

Open in a new tab

This svg element has an empty ("") accessible name because it has no attributes or content to provide an accessible name.

<html lang="en">
	<p>Happy new year!</p>
	<svg height="200" xmlns="http://www.w3.org/2000/svg">
		<polygon points="100,10 40,180 190,60 10,60 160,180" fill="yellow" />
	</svg>
</html>

Inapplicable Example 4

Open in a new tab

This canvas element has an empty ("") accessible name because it has no attributes or content to provide an accessible name.

<html lang="en">
	<p>Happy new year!</p>
	<canvas id="newyear" width="200" height="200"></canvas>
	<script>
		const ctx = document.querySelector('#newyear').getContext('2d')
		ctx.fillStyle = 'yellow'
		ctx.beginPath()
		ctx.moveTo(100, 10)
		ctx.lineTo(40, 180)
		ctx.lineTo(190, 60)
		ctx.lineTo(10, 60)
		ctx.lineTo(160, 180)
		ctx.fill()
	</script>
</html>

Inapplicable Example 5

Open in a new tab

This img element is not visible.

<html lang="en">
	<img src="/test-assets/shared/w3c-logo.png" alt="W3C logo" style="display:none" />
</html>

Inapplicable Example 6

Open in a new tab

This canvas element is not visible because it is completely transparent.

<html lang="en">
	<canvas width="200" height="200"></canvas>
</html>

Inapplicable Example 7

Open in a new tab

This img element has no accessible name because it is not included in the accessibility tree.

<html lang="en">
	<img aria-hidden="true" src="/test-assets/shared/fireworks.jpg" alt="fireworks" />
</html>

Inapplicable Example 8

Open in a new tab

This svg element is ignored because it is a child of a link that provides its accessible name.

<a href="https://w3.org" aria-label="W3C Website">
	<svg height="200" xmlns="http://www.w3.org/2000/svg" aria-label="star">
		<polygon points="100,10 40,180 190,60 10,60 160,180" fill="yellow" />
	</svg>
</a>

Inapplicable Example 9

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This img element has a src attribute which will cause the image request state to be Broken.

<img src="/test-assets/does-not-exist.png" alt="" />

Inapplicable Example 10

Open in a new tab

This is a div element with a background image. Background images must be tested separate from this rule.

<p>Happy new year!</p>
<div
	style="
	width: 260px;
	height: 260px;
	background: url(/test-assets/shared/fireworks.jpg) no-repeat;
"
></div>

Glossary

Accessible Name

The accessible name is the programmatically determined name of a user interface element that is included in the accessibility tree.

The accessible name is calculated using the accessible name and description computation.

For native markup languages, such as HTML and SVG, additional information on how to calculate the accessible name can be found in HTML Accessibility API Mappings 1.0, Accessible Name and Description Computation (working draft) and SVG Accessibility API Mappings, Name and Description (working draft).

For more details, see examples of accessible name.

Note: As per the accessible name and description computation, each element always has an accessible name. When no accessible name is provided, the element will nonetheless be assigned an empty ("") one.

Note: As per the accessible name and description computation, accessible names are flat string trimmed of leading and trailing whitespace. Notably, it is not possible for a non-empty accessible name to be composed only of whitespace since these must be trimmed.

Explicit Semantic Role

The explicit semantic role of an element is determined by its role attribute (if any).

The role attribute takes a list of tokens. The explicit semantic role is the first valid role in this list. The valid roles are all non-abstract roles from WAI-ARIA Specifications. If the element has no role attribute, or if it has one with no valid role, then this element has no explicit semantic role.

Other roles may be added as they become available. Not all roles will be supported in all assistive technologies. Testers are encouraged to adjust which roles are allowed according to the accessibility support base line. For the purposes of executing test cases in all rules, it should be assumed that all roles are supported by assistive technologies so that none of the roles fail due to lack of accessibility support.

Focusable

An element is focusable if one or both of the following are true:

Exception: Elements that lose focus during a period of up to 1 second after gaining focus, without the user interacting with the page the element is on, are not considered focusable.

Notes:

Included in the accessibility tree

Elements included in the accessibility tree of platform specific accessibility APIs are exposed to assistive technologies. This allows users of assistive technology to access the elements in a way that meets the requirements of the individual user.

The general rules for when elements are included in the accessibility tree are defined in the core accessibility API mappings. For native markup languages, such as HTML and SVG, additional rules for when elements are included in the accessibility tree can be found in the HTML accessibility API mappings (working draft) and the SVG accessibility API mappings (working draft).

For more details, see examples of included in the accessibility tree.

Programmatically hidden elements are removed from the accessibility tree. However, some browsers will leave focusable elements with an aria-hidden attribute set to true in the accessibility tree. Because they are hidden, these elements are considered not included in the accessibility tree. This may cause confusion for users of assistive technologies because they may still be able to interact with these focusable elements using sequential keyboard navigation, even though the element should not be included in the accessibility tree.

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:

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.

Programmatically Hidden

An HTML element is programmatically hidden if either it has a computed CSS property visibility whose value is not visible; or at least one of the following is true for any of its inclusive ancestors in the flat tree:

Note: Contrary to the other conditions, the visibility CSS property may be reverted by descendants.

Note: The HTML standard suggests setting the CSS display property to none for elements with the hidden attribute. While not required by HTML, all modern browsers follow this suggestion. Because of this the hidden attribute is not used in this definition. In browsers that use this suggestion, overriding the CSS display property can reveal elements with the hidden attribute.

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.

Content is defined in WCAG.

For more details, see examples of visible.

WAI-ARIA specifications

The WAI ARIA Specifications group both the WAI ARIA W3C Recommendation and ARIA modules, namely:

Note: depending on the type of content being evaluated, part of the specifications might be irrelevant and should be ignored.

Rule Versions

  1. Proposed version, 30 August 2023 (compare)
  2. Latest version, 30 August 2023

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.

Implementation Type Consistency Report
Axe DevTools Pro 4.37.1 Semi-automated tool Consistent Axe DevTools Pro Report
Trusted Tester 5.1 Test methodology Consistent Trusted Tester Report
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