Thanks to Ralf (Be aware, mostly numbers on that weblog!), I just stumbled across Retrievr. Retrievr is a search engine that searches for images on flickr. The cool thing about it is that you can search by painting images that look similar to what you're looking for.

Although the search still seems to be based on color mainly instead of form, it already looks quite useful.

I still wonder how to save images from flickr to my desktop machine. They somehow seem to block this with some JavaScript or HTML layer tricks. I don't want to look at the HTML code everytime I save something.