For some time, Google Labs has been testing search algorithms designed to find similar images, and yesterday announced that the feature is now a permanent fixture on Google Image Search.
As you’d expect, it’s a great way to narrow down images after searching for a broad topic, in much the same way as you’d do with text-based searches. It also helps when a word can have multiple meanings, such as “jaguar” or “keyboard”.
Unfortunately, I’ve only got Google’s word on this at present as I’m not seeing any “find similar images” links, even on the examples Google provided, but it certainly sounds like a really useful addition.