What is Alt Text?
A description of a graphic, which usually isn’t displayed to the end user, unless the graphic is undeliverable, or a browser is used that doesn’t display graphics. Alt text is important because search engines can’t tell one picture from another.
Alt text is the one place where it is acceptable for the spider to get different content than the human user, but only because the alt text is accessible to the user, and when properly used is an accurate description of the associated picture. Special web browsers for visually challenged people rely on the alt text to make the content of graphics accessible to the users.