WAI compliance

So that output from your DITA source meets accessibility responsibilities, you must include alternative text representations of all images in DITA content.

Graphics in HTML and other online formats must have alternative text representations in order to comply with Web Accessibility Initiative (WAI) guidelines (and national laws, such as US Section 508).

You must include alternative text representation values in the alt attribute of all image elements.

If the images are purely presentational in nature, they should be applied via CSS (in the presentation layer). When an image is specified within a CSS, there is no capacity to specify alternative text; such images are considered to be simply decorative. This does not breach the WAI recommendations.

When graphics are used to denote notes, warnings, etc, it could be argued that the images contain meaning. Therefore, CSS should not be used to place such images; the HTML img element, with a descriptive alt attribute, should be used. These labels will be applied by the DITA publishing process; as a DITA author, you only need to apply the correct semantic mark-up, such as the note element and its type attribute.