How does it work and how can i take advantage of this i hear you ask?
Googlebot is the bot that crawls the web, indexing images just like the regular Googlebot indexes pages and keywords for the normal search index. Yes the two are different bots, however the Google Image bot is very slow and doesn't visit a site with anywhere near the frequency as a regular Google search bot.
Because Google can't actually "see" images like we can (yet), it relies on a number of factors to help determine what an image is all about.
What are these factors?
These include things such as Alt Text, File Names, Surrounding Text, Page Title, Page Theme as well as links.
Some brief hints are:
Alt Text - Try to be descriptive with your Alt Text, however don't over do it. Also try not to include too many "junk" words like, the, and, or, we, are, for, etc.
File Name - Try to keep the File Name either the same, or very similar to the Alt Text. Don't try and rank the same image for multiple terms by jamming different keywords in the Alt and File Names.
Surrounding Text - Always try and place a paragraph of descriptive text directly above and below your image, with the keyphrase from your Alt Text and Image Name included in this text.
