See Understanding Techniques for WCAG Success Criteria for important information about the usage of these informative techniques and how they relate to the normative WCAG 2.0 success criteria. The Applicability section explains the scope of the technique, and the presence of techniques for a specific technology does not imply that the technology can be used in all situations to create content that meets WCAG 2.0.
HTML and XHTML
This failure relates to:
This describes a failure condition for text alternatives on images. If there is no source of text to provide an alternative for the image then assistive technologies are not able to identify the image or to convey its purpose to the user. The alt attribute continues to be the preferred way to provide alternative text for images. Appropriate WAI-ARIA attributes may be used to provide alternative text, as long as they are accessibility supported. For more information about accessibility support, see Documenting Accessibility Support. The Accessible Rich Internet Applications (WAI-ARIA) 1.0 Specification describes the Text Alternative Computation, for computing the text alternative from the HTML and WAI-ARIA attributes of an element.
Some Assistive Technologies attempt to compensate for the missing text alternatives by reading the file name of the image. But it is insufficient to rely simply on the file name for many reasons. For example, file names may not be descriptive (e.g., images/nav01.gif), and technology specifications do not require descriptive file names. And some Assistive Technologies do not read the file name if there is no text alternative provided via HTML attributes.
In the code example below, the person using a screen reader would not know the purpose of the image.
Example Code:
<img src="../images/animal.jpg" />
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Identify img, area and input elements of type "image". For each of these elements:
Check if the alt attribute is present.
Check if aria-labelledby attribute is present AND references one or more id elements in the page AND check if aria-labelledby is accessibility supported.
Check if the aria-label attribute is present AND check if aria-label is accessibility supported.
Check if the title attribute is present AND check if title is accessibility supported.
If all of #1, #2, #3 and #4 are false then this failure condition applies.