Metapixel is a photomosaic generator. 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 substituted, as well as collage-style photomosaics, where
the images are placed at arbitrary positions in the source
image, not aligned to a matrix.

WWW: http://www.complang.tuwien.ac.at/~schani/metapixel/