generator for photomosaics

 Metapixel is a program for generating photomosaics. It can generate
 classical photomosaics, in which the source image is viewed as a matrix
 of equally sized rectangles for each of which a matching image is
 substitued, as well as collage-style photomosaics, in which rectangular
 parts of the source image at arbitrary positions (i.e. not aligned to a
 matrix) are substituted by matching images.