WCAG Techniques for image text alternatives
For many years the main way to provide a text alternative for an image was to use the
alt attribute. This has changed with the advent of WAI-ARIA.
alt is still a valid, well supported attribute and is often one of the first things that developers learn to use when they create accessible web content.
ARIA provides additional ways to describe what an image is. When there is related text on a page, the
aria-labelledby attribute can be used to join in-page descriptions and images, and the
aria-label attribute can provide a textual value for assistive technologies to read.
The alt attribute has some advantages:
alt is used not only by screen reader users but also search engines for indexing purposes;
alt is very well supported by browsers and assistive technologies; and
alt is shorter to type than
aria-labelledby. But even with these advantages, authors have expressed an interest in using ARIA.
The Web Content Accessibility Guidelines (WCAG) Working Group is working on an update to two non-normative documents, Techniques for WCAG 2.0 and Understanding WCAG 2.0, and discussed extensively whether ARIA is sufficiently ready to suggest that authors use it now, as a part of their workflow.
In order to ensure our non-normative supporting documents are progressive and up to date with new accessible design patterns - the WCAG Working Group requested public comment on two techniques, ARIA 10 and F65.
The technique ARIA10, which originally recommended use of the
aria-labelledby attribute for any type of non-text objects, in order to meet WCAG success criteria 1.1.1, was modified during the commenting period to only apply to non-text objects - that do not already allow the use of the
alt attribute. This restriction in the use of
alt may be due to some limitation in the authoring environment for example.
Also F65, a failure technique, previously stated that any image (<img>, <area>, and <input> of type "image") that is missing the
alt attribute would fail success criteria 1.1.1. The Working Group therefore modified F65 so that images that do not have an
alt attribute but do use
aria-label will not automatically fail the success criteria, provided that the author finds that there is sufficient accessibility support for the ARIA attribute used.
The result of these two changes is that the Working Group is recognising that authors need and want to use ARIA attributes. Given the evolving level of accessibility support the group then decided to:
- Allow the responsible use of ARIA attributes for images when accessibility supported (by no longer failing images using aria attributes even if they do not use
- Stop short of fully recommending only the use of ARIA attributes on images (by not including a sufficient technique that would encourage this practice).
As the level of accessibility support for ARIA continues to improve, the Working Group expects to develop additional techniques. It is expected that as accessibility support for
aria-labelledby improves that a sufficient technique for using ARIA attributes image accessibility will be published.
Thoughts and comments welcome!