Dwarven Mosaic Assistant is a program designed to make turning external images into a beautiful mosaic for your fortresses a little easier. It simply divides a given picture into given size tiles and approximates the closest color found in DF.
The program is currently in its infancy, but should be reasonably functional. It will be upgraded later if there is demand.
Currently the program uses Simple Directmedia Layer, which you can get from www.libsdl.org. It's free and available on all platforms.
-Nahkh

(I included a windows binary as well as the source. It should compile on other systems with minimal effort.)