Sample images
Tump is a free opensource program to generate mosaic pictures, written by Juho Roine.
Important: Tump can be now considered as dead since there already exists a better alternative: Metapixel. I originally wrote Tump because I wasn't aware of any other such gpl'ed programs. Source code of Tump is left on the net for public interest.
Tump uses Imagemagick to perform image operations. It is developed on Linux, but should run on any Unix.
Download sourcecode (tump-0.1.1.tar.gz)
Contact author: tump at juhoroine dot net. Feedback etc. would be nice.