Google Releases Reverse Image Search
A new feature in Google's image search engine now lets you upload or link an image to find out where else it's been used on the Web. To use this feature, simply go to images.google.com, click on the camera icon, and select "Upload an image". Alternatively, if you've a URL of an image, select "Paste image URL" instead. You could search by image even faster by using either a Chrome extension or Firefox extension.