Way back in April, Google relaunched Google Labs, the place where the company tests its new and experimental features. When it relaunched, it added a very interesting experimental feature to Google Image Search:
A recap if you don't remember similar images: it utilizes image recognition technology to help filter search results. If you find an action shot of soccer/football star David Beckham and want to find more like it, for example, you can use Similar Images to filter your results and find similar images.
The feature has been in Google Labs for over half a year, but that's no longer the case. Google has announced that Similar Images has now become a standard feature of Google Image search.