Google is rolling out search by image feature to desktop. With this feature enabled you can search for an image by any of the following method on images.google.com.
Drag and drop an image from the web or your computer into the search box or
On images.google.com, click the camera icon, then select “Upload an image.” Select the image you want to use to start your search or
Found an image on the web you’re curious about? Right-click the image to copy the URL. On images.google.com, click the camera icon, and “Paste image URL” or
Use the official Google add-on for * Firefox and Chrome. With the Search by Image extension installed, simply right-click an image on the web to search Google with that image.
How Google Search By Image Works?
“Google uses computer vision techniques to match your image to other images in the Google Images index and additional image collections. From those matches, we try to generate an accurate “best guess” text description of your image, as well as find other images that have the same content as your search image. Your search results page can show results for that text description as well as related images.”
Note : Extension will be fully functional at 6 PM, PST on June 15, 2011.
* Firefox 5 not supports. [Via]
[...] update. Anyway Google has already introduced image search and hope you all will satisfied with Google Image search. #dd_ajax_float{ background:none repeat scroll 0 0 #FFFFFF; border:1px solid #DDDDDD; float:left; [...]