Some things just don't work well enough. Tim Brays Cherry-Tomato Challenge revolves around finding just one example of a search engine that uses the img tag's title or alt attributes as search guides in image search. He's harped on this before, but this seems like a good one to watch. As a testament to how fantastic they seem, I'm a but surprised Google didn't fix this after the last time it got a mention on Bray's blog.
[UPDATE (as of 2006-02-11, but it has been fixed for a while) : Google does this right]