Google:Search by Image
There are three ways to search by image:
* Drag and drop
* Upload an image
* Copy and paste the URL for an image
"After a photo is added to the search box, Google delivers relevant results related to it. So, if a person drops a picture of a location in the search box, for example, Google will return information about the place, as well as any Web results on the same topic."
To search by image even faster, download the Chrome extension or the Firefox extension. With the extension installed, simply right-click an image on the web to search Google with that image.