The video of [Thibault Brevet's] printer makes it look like he’s actually designed a vinyl cutter (watch it after the break). But at the end of the printing process you see that the top layer was actually a piece of carbon copy paper and the magic was happening underneath. The print head applies enough pressure to transfer the blue-ish printing ink onto the paper giving the result seen above. He’s driving this with an Arduino and feeding data using Processing.
[Thibault] left this link in the comments from the LEGO printer post. Shame on him for not tipping us off as soon as he posted info on this hack. Don’t underestimate yourselves, if you hack it we want to hear about it!