Google Labs released a new experimental service “Similar Images” that lets you find similar images related to the search you are doing. Search for a word and then click on similar image link below the image and it returns similar images, the tool so far works perfectly.
For example searching for Paris results both Eiffel tower and Paris Hilton images, but if you select similar images link below the Eiffel tower image you will get only the images of Eiffel. This service is useful if you are searching for a better image of something, instead of searching in Google images and browsing for pages, you can hot similar images and select the best one.
See the video that describes this feature.
Via Google Blog