Normally, an image search involves inputting text with the output being images, however, a reverse image search allows the user to input an image with the output being the website(s) that have that (or a similar) image, the uses range from finding a higher quality image, finding the original source or simply finding out exactly what that image is.
It is nothing new, for example Tineye, however, Google already has a well developed image cache which allows it to far exceed the likes of Tineye.
Google Images
Extra information
It is nothing new, for example Tineye, however, Google already has a well developed image cache which allows it to far exceed the likes of Tineye.












