Algorithm for finding similar images If you go to FFFFOUND! and click on some image you will notice that on the new page, under the image, there is a section called "You may like these images." which suggests 10 images that look similar to the original.

What would be a good algorithm to achieve this functionality for a collection of images?

Any documentation, books, etc. related to such algorithms is very appreciated. Also algorithms for finding similar images that yield better results than those seen on FFFFOUND! website are also welcome.
You could take a collective intelligence approach and try to determine similarity between various users based on their tastes of other images. If I like a bunch of images and another user likes majority of the same images, then it could be said that I will most likely like pictures the other user likes.

You might want to try and find information on Collaborative Filtering, Euclidean Distance/Pearson correlation (within the context of social networks.)