There's always a guerrilla undercurrent with graffiti, but the Facade Printer, which uses a computer-enhanced paintball gun to tattoo images onto buildings, really makes that aspect explicit. Judging by its work, it appears to have pretty good aim.
The German contraption, which is comprised of an pressurized barrel mounted on a two-axis turntable, can blast pictures onto walls from a distance of 20 feet. It's controlled by an on-board industrial PC running a custom touch interface.
Images can be loaded onto the machine with a USB stick, and they're printed by paintballs of many colors traveling over 100mph.
The Facade Printer is an especially cool embodiment of the push to make art, not war. Of course, it's hard not to imagine how much havoc it could wreak in your local paintball league. More pictures and video at DesignBoom.