When using the img element, specify a short text alternative with the alt attribute or use an empty alt in case of a decorative image. When an image contains words that are important to understanding the content, the alt text should include those words. This will allow the alt text to play the same function on the page as the image. Note that it does not necessarily describe the visual characteristics of the image itself but must convey the same meaning as the image.
Engine scans the page for
<img> elements which are not the child of a link and are missing an alt attribute
The intent of this is to make information conveyed by non-text content accessible through the use of a text alternative. Text alternatives are a primary way for making information accessible because they can be rendered through any sensory modality (for example, visual, auditory or tactile) to match the needs of the user. Providing text alternatives allows the information to be rendered in a variety of ways by a variety of user agents. For example, a person who cannot see a picture can have the text alternative read aloud using synthesized speech.
<img src="/CrossingDeleaware.jpg" alt="Painting of George Washington crossing the Delaware River"/>