There are various search engine technologies to search for images. This may happen by indexed images and tags or by advanced technologies using image recognition. The latter does the new image search engine GazoPa.
GazoPa offers various ways to search for images by having a key feature called similarity search. So images may either be found by keywords or by supplying an image to find similar looking ones. The latter may happen by uploads, linking to an image on the web or drawing.
Further tools are available at the search results pages with a matching tool for images and videos seeming to be most remarkable and useful. So one may provide an image to find a relating video. Too, at the results pages a search query may become modified and if a suitable image has been found, it may be posted to Twitter or Facebook.