Right now, if you want to search for an image, you are limited to searching using keywords. TinEye is a new and possibly revolutionary visual search engine currently in beta testing.
Start at: www.tineye.com.
The idea is to give the site an image and it will tell you where that image appears on the web. The possibilities for finding imagery (and controlling the use of your imagery) are enormous. Many of us are waiting to see if this works out to be half as good as it sounds.