I’m not sure if Retrievr has any commercial application, but it is a really beautiful piece of technology.
Retrievr has a Flash sketch pad built into the site. Draw something – anything – and it will fetch Flickr images that are similar. My very rough drawing of a black line intersecting with a red blog brought up some nice results (see image).
More information is available on their about page, here. Thanks Nivi for pointing this out to me (and I aplogize again for using your “special” towel to dry off Laguna’s feet :-) ).