In Google’s webmaster guidelines, they advise the use of alternative text for the images on your web site:
Images:. Use the alt attribute to provide descriptive text. In addition, we recommend using a human-readable caption and descriptive text around the image.Why would they ask us to do that? The answer is simple, really; search engines have the same problem as blind users. They cannot see the images.
Many webmasters and inexperienced or unethical SEOs abuse the use of this attribute, trying to stuff it with keywords, hoping to achieve a certain keyword density, which is not as relevant for rankings now as it once was.
On the contrary, high keyword density can, on some search engines, trigger spam filters, which may result in a penalty for your site’s ranking. Even without such a penalty, your site’s rankings will not benefit from this tactic.
This method also puts persons who use screen readers at a greater disadvantage. Screen readers are software-based tools that actually read aloud the contents of what is displayed on the screen. In browsing the web, the alt attributes of images are read aloud as well.
Imagine listening to a paragraph of text which is followed by repetitions of many keywords. The page would be far from accessible, and, to put it bluntly, would be found quite annoying.
Jonhnson Frederic Merchadou Emilia Lambert Jacques & Co
