For those of you interested in this subject, there is a library called LIRE (http://www.semanticmetadata.net/lire/ http://www.semanticmetadata.net/lire/) that's

For those of you interested in this subject, there is a library called LIRE (http://www.semanticmetadata.net/lire/ http://www.semanticmetadata.net/lire/) that's been around for a long time which will index various color and textures features into a feature vector compatible with Lucene. It does end up with the interesting scenario of requiring the search query itself to be an image, but if you are looking for a solution whereby for a given image you can find other images most similar to it (and ranked, of course), this does the job surprisingly well.