I have no earthly clue how they did this, but Retrievr is an absolutely amazing application that searches flickr based upon drawings that you create. For example, draw a smiley face and it will return pictures of people or other animals smiling. Dray a frowining face and it will return pictures of people/animals frowning. The more artistically inclined you are, the better results you will get, but it works even for the most crude drawings. Check it out!