The need to provide a text-based description of images to those who are unable to see the images is one of the most important principles of accessibility. In fact, it is the very first guideline listed in WCAG 2.1 (Web Content Accessibility Guidelines)—Guideline 1.1.1.
“All non-text content [e.g. images, animations, and video images] that is presented to the user has a text alternative that serves the equivalent purpose.”
Many authors and developers understand the purpose of providing alternative text or “ALT text,” but determining what to write as the ALT text can be a little confusing at first. A single image could have many descriptions of varying lengths—hence the traditional saying “A picture is worth a 1,000 words.”
The key to writing high-quality ALT texts and other image descriptions is to determine how the image contributes to the content of the document. Does the image provide additional information or critical information? Or does it just add visual interest? If the image is not decorative, then how does it relate specifically to the information in the document? The answer to these questions serves as guide in providing a usable image description. The scenarios below show how to analyze the combination of document purpose and existing text to decide on an appropriate description.
Elizabeth J. Pyatt is an ALT Media and Accessibility Specialist at Penn State and has developed alternative text descriptions for a wide variety of subjects and document types over the past two decades.
- Does the image provide additional information or critical information?
- Or does the image just add visual interest?
- If the image is not decorative, then how does it relate specifically to the information in the document?
- What are some strategies to provide complex descriptions?