The text in the ADA did not originally mention websites since this technology was not widely used in 1990. But now that most businesses have a website, they need to make sure it’s accessible to everyone. Since we’re past the ruling date, all updated pages on your website are required to be at least grade A complaint, with grade AAA being the highest.
The words in the tag should be more than a description. They should provide a text equivalent of the image. In other words, the tag should include the same meaningful information that other users obtain by looking at the image. In the example of the mayor’s picture, adding an “alt” tag with the words “Photograph of Mayor Jane Smith” provides a meaningful description.