First discovered by Tara (and also blogged by Barry, Philipp, and John) is an experimental search tool called retrievr that allows the user to find related Flickr images by drawing a sketch. Barry writes that it doesn't work too well while Philipp is more postitive. Tara notes it works well for browsing.
The concept of sketching/drawing to find imagery is not new.
Experimental work in this are has been going on at Purdue University for several years. Here are a few related links, papers, and a small demo.
Researchers at Purdue University have been doing work in this area for several years. Here are some useful links.
+ 3D Searching starts to take shape
From Computer.org (PDF)
While we're on the subject of image search demos, this one from LTU Technolgies is also cool. Keyword search royalty free images from the Corbis catalog and then find visually similar imagery using LTU's "image DNA" technology. Want to learn more. See this post.