This is really neat. Mike Arrington pointed me to Retrievr -- you draw something in the Retrievr sketch pad and then is searches something similar.
Mike explains:
Retrievr has a Flash sketch pad built into the site. Draw something - anything - and it will fetch Flickr images that are similar.
try it ... very impressive. we're getting closer and closer to fast image recognition technology which will totally change the way we process and search pictures, photos, videos, etc.