Image ALT Attributes

The Google webmaster site has a useful Youtube Video explaining the importance of altTags not only to enhance accessibility, but also because “providing useful, accurate information in your ALT attributes can make your photos and pictures more discoverable on the web.” Mozilla have provided an example of alt text in the image below as "Grapefruit slice atop a pile of other slices"

alt text example Grapefruit slice atop a pile of other slices

“The alt attribute is defined in a set of tags (namely, img, area and optionally for input and applet) to allow you to provide a text equivalent for the object.” (W3C tutorial aout Image Concepts)

The importance of adding alternative text may be lost in the hurry to add photos and graphics to websites that are built by using online page makers or working in wikis and blogs often associated with templates and rich text editors. However, as Webaim state “Adding alternative text for images is the first principle of web accessibility. It is also one of the most difficult to properly implement. The web is replete with images that have missing, incorrect, or poor alternative text. Like many things in web accessibility, determining appropriate, equivalent, alternative text is often a matter of personal interpretation. Through the use of examples, this article will present our experienced interpretation of appropriate use of alternative text.”


It is possible to use the Webaim Wave online checker to look for missing alt attributes or as suggested by Patrick Lauke the Web Developer add-on for Firefox. However, automatic checkers cannot tell you whether they are appropriate or relevant, this has to be done by listening to the output of screen reading software whilst checking the images.

Terrill Thompson uses the Web Accessibility Toolbar (WAT) to generate a list of images and their alt texts, but as he says you still have to ‘critique the use of alt texts for meaningful texts and proper use of null texts’. (There is a similar toolbar for Firefox - the Firefox Accessibility Extension)

Example of JAWS reading an image caption by Karen Sorensen



This technique may be used to test the following section of best practice.

Document Section Heading
WCAG 2.1 1.1.1 Non-text Content More Info