I used a google paper's approach in a mosaic competition. I didn't end up submitting it, but I got it working. It uses locality sensitive hashing to hash vecto

I used a google paper's approach in a mosaic competition. I didn't end up submitting it, but I got it working. It uses locality sensitive hashing to hash vectors into buckets. These buckets are a subset of the total set of items. It worked with similar images of a small size when I used it, but I didn't have many images. In my case, the vectors were just the rgb values of the down-sampled image.