Describe complex images by their purpose or nature
no. 054
Make sure complex images have alt attribute values that properly describe their purpose
Sometimes, images are so complex that attempting to describe the information they contain in a regular ALT attribute value is just counter productive. Whether because providing the description would be too long, or because it requires some form of structure that is just not possible in a simple ALT value text string. In such cases, it is better to use the ALT attribute value to describe the purpose or nature of the image, and use another mechanism to actually describe the content the image displays.
To do so, simply describe the nature of the image using an ALT attribute value, rather than the information that is being displayed. For example, a graph containing a lot of structured information about the prevalence of disability in ageing populations based on age groups and disabilities would be better off described as simply “a graph about X”, rather than attempting to load all the graph’s information into the ALT value. Providing a second mechanism to actually describe the image, whether this mechanism is linked from the image or is available as adjacent information next [...]