About a month ago I wrote about Multicolor search lab, a tool that let's you search Flickr images by selecting a colour palette.
Today I stumbled over another oldie-but-goodie, based on the Flickr API. retriever gives you a simple little tool to draw colour sketches, which are then matched to images in Flickr. Your drawings automatically generate urls: this was my attempt to get buildings at night time.
Again, imagine - just imagine - if you applied this search tool to your online collection. Is it for the hard core researcher? No. Is it an engrossing search experience? Yes.