Technique ARIA15:Using aria-describedby to provide descriptions of images

Applicability

Technologies that support Accessible Rich Internet Applications (WAI-ARIA).

This technique relates to 1.1.1: Non-text Content (Sufficient).

Description

The objective of this technique is to provide descriptions of images when a short text alternative does not adequately convey the function or information provided in the object.

A feature of WAI-ARIA is the ability to associate descriptive text with a section, drawing, form element, picture, and so on using the aria-describedby property. This is similar to the longdesc attribute in that both are useful for providing additional information to help users understand complex images. Like longdesc, descriptive text provided using aria-describedby is separate from the short name provided using the alt attribute in HTML. Unlike longdesc, aria-describedby cannot reference descriptions outside of the page containing the image. An advantage of providing long descriptions using content from the same page as the image is that the alternative is available to all, including sighted people who do not have assistive technology. It is worth noting that as of the time of writing (October 2013) some assistive technologies read aria-describedby content immediately after an image's alt attribute information without user activation - whereas most implementations of longdesc require the user to take explicit action to read the additional description.

Like aria-labelledby, aria-describedby can accept multiple ids to point to other regions of the page using a space separated list. It is also limited to ids for defining these sets.

Examples

Example 1: Describing an image

The following example shows how aria-describedby can be applied to an image to provide a long description, where that text description is on the same page as the image. 

<img src="ladymacbeth.jpg" alt="Lady MacBeth" aria-describedby="p1">
<p id="p1">This painting dates back to 1730 and is oil on canvas. It was created by 
Jean-Guy Millome, and represents ...</p>

Other sources

No endorsement implied.

Tests

Procedure

  1. Examine each image element where a aria-describedby attribute is present.
  2. Examine whether the aria-describedby attribute programatically associates an element with its text description, via the id attribute on the element where the text to be used as the description is found.
  3. Examine whether the combined text equivalent and associated text description accurately describe or provide the equivalent purpose to the object.

Expected Results

  • #1, #2, and #3 are true.