Korge, I'm volunteering to help with this.
Photographs like these are probably fine if you can make them on clean, non-USPS-envelope (lol) paper. I may be able to run it through Photoshop's Posterize tool, which should reduce it to the "basic" 16 colors - it may not work as some quality may be lost, and I'll have to re-clean-it-up / de-pixellize it a bit, but hey, this stuff is great (for graffiti anyway, I'm obviously not familiar with graffiti and unsure how to rate it).