You have probably searched for images on google image search before, but what you probably missed was the drag and drop image search feature. After hovering over an image from the image search results (ex: http://goo.gl/hwiJ0) drag the image over to the search text box. Once the image overlaps the search box, the search box extends allowing you to “drop the image” there.
What seems to happen next is google uses meta data about the image selected to generate a text search that display results of web sites that are related to the picture.
There was a google labs project a while back that gamified the manual tagging of images, mechanical turk style. Maybe this is one of the bi-products of that project.