Add Descriptive Text to Images for Better Search Engine Results
Search engine spiders are pretty smart, but they can’t see images that you add to your Web pages — not yet, anyway. This means that when you include pictures in your Web site, you should give them useful and relevant filenames, and also describe them in both the surrounding text and the Alt attribute text.
There are several places where you can put descriptive text around your images so that search engines can read it. You can refer to what the image is about in the following locations:
Text surrounding the image. Include descriptive text above, below, or next to the picture. A caption or a lead-in sentence that explains what the image shows works well. This gives search engine spiders text they can read and index, but it also helps communicate your intended meaning to users.
Filename. The filenames of your images should contain descriptive words.
Alt attribute. You can also put brief descriptive text into the Alt attribute attached to any image. For example, alt="1968 Ford Mustang California Special Gas Cap".
Because both people and search engines are going to read your filenames, be sure to use good, descriptive words in your image files. Here is another opportunity to provide readable content (with keywords, if appropriate) to the spiders. Instead of naming your image A1234.jpg, call that photo of a skier falling on his face skier-faceplant.jpg so the search engines know what it is, too.
To separate words, don’t use a space or an underscore (underscores are seen as an alpha character, rather than as punctuation). Instead, use a hyphen or a period to separate words in your filenames. But try not to overuse them either — just because you can have many dashes in a URL doesn't mean that you should.
Also, keep filenames brief. Remember that long filenames cause URLs to get longer, too (such as if one of your images gets returned in an image search). Because people generally avoid clicking long URLs, keep your names to a reasonable length. Six words in a filename would generally be too much. Keep it simple: a picture of a Ford mustang with a dented fender shouldn't be called fordmustang-with-a-dented-fender.jpg, just call it dented-ford-mustang or mustang-dented-fender.jpg. You'll have on-page text and Alt attributes to explain to the engines what the content of the image is.