Any page image has a special optional attribute known as "alternative text.” It is specified using the HTML «ALT» tag. This text will be displayed if the browser fails to download the image or if the browser image display is disabled. Search engines save the value of image ALT attributes when they parse (index) pages, but do not use it to rank search results.

Currently, the Google search engine takes into account text in the ALT attributes of those images that are links to other pages. The ALT attributes of other images are ignored. There is no information regarding other search engines, but we can assume that the situation is similar. We consider that keywords can and should be used in ALT attributes, but this practice is not vital for seo purposes.