This may not be what you’re looking for, but we normally recommend StippleGen– a utility that we built for this very purpose — which can convert jpg files to black and white stipple or TSP drawings that can be drawn very well by an Eggbot:  http://wiki.evilmadscientist.com/StippleGen

Two good examples from other folks as well:

http://www.flickr.com/photos/lodefink/8602880115/in/pool-eggbot

http://www.flickr.com/photos/75390883@N06/8559930536/in/pool-eggbot