Google Image Search borrowed a Bing feature i.e. "when you mouse over an image on results page, there's a new option called "more sizes" that lets you find other versions of the same image". This's useful if you want to find higher-quality version of an image or if you want to list all the sites that include a certain image.
A similar service is TinEye, a search engine that finds different versions of an image you upload. "TinEye is a reverse image search engine. It finds out where an image came from, how it is being used, if modified versions of the image exist, or if there is a higher resolution version."