Okay, hardly an original idea, but I've seen it elsewhere (see Gerry's Graffiti!), I loved the concept and I have many creative and artistic friends. All ya gotta do is download the image, edit it with the paint program of your choice (it's gotta be able to handle jpeg's) and then e-mail it to me. Go for it.

Thanks to my friend Emrys for adding the latest graffito:
I'll be back. Wait for me. -Godot