One of the largest accessibility challenges with online content today is the lack of alternative text for images and image maps. Sight-impaired users often use screen readers or refreshable Braille devices to read online content. However, when these assistive technologies come across images or image maps without alternative text, also known as alternate text, they are unable to provide users with information about the image or image map and its meaning.

The Web Content Accessibility Guidelines require that alternate text be provided for all images and image maps in online content. The alternate text is an image label that describes the image or each area of the image map. Online content should display alternate text for images and image maps when users perform the following actions:

The alternate text you assign to an image or sections of an image map should be as accurate and as succinct as possible and provide users with a brief description of the image and how the image relates to the page they are viewing. Make sure that your alternate text conveys all of the important information related to the image or image map section, but do not burden users with excessively long alternative text. Screen readers or refreshable Braille devices always read the alternative text, so if your page has several images or complex image maps with long descriptions, it can take a long time for the assistive devices to read image-heavy pages with long descriptions. If you need to provide a description of the image or image map section that is more than a few words or a few short sentences, you should provide a brief alternate text description of the image or image map section and then assign a longer description the image using either the longdesc attribute or a description. Once you specify a long description using the longdesc attribute, you can also optionally display a D link next to the image. For more information about assigning long descriptions to images, see Assigning Long Descriptions to Images in Word.