I've finally posted some of my older existing C code on BartForge. My Netpbm ASCII Art package provides the ability to create decent-looking ASCII art images from your pictures, and the ability to turn an existing piece of ASCII art back into a decent-looking picture.
These are tools that are based on the Netpbm package of pipeline-oriented image processing utilities. There are a number of archives of ASCII art online to play with, but I'm not sure which one to point you at. Enjoy. (B)