Your arm moves the printer head in this home-made hand-held ink jet printer. Devised by a Dutch hacker, he calls it an electronic stamp. It can print on paper, white board, a balloon - anything you can move your arm over.
He writes on his blog, Sprites Mods, "In a normal inkjet printer the print head is moved back and forth with a motor and a guiding system. If however, we want to make a manageable device then it is not convenient to integrate this entire system into an electronic stamp. That is why we use only the cartridge together with some electronics that drives the head. Moving the head itself is a job for the user. When moving it is important to hold the whole assembly straight and move with a uniform motion across the surface. After a little practice this is quite easy to do.