The world's first industrial robot tattoo robot has been created by French designers Pierre Emm and Johan da Silveira (otherwise known as Appropriate Audiences).
(Industrial robot tattoo artist video)
As the video explains, the process of tattooing by robot has a few steps. You've got to create a 3D scan of the target area, mock up the desired tattoo using custom computer software, and then (as we mentioned before) make sure the recipient stays very, very still. After all, industrial robots are incredibly precise, but most models are not at all responsive. That's why people are killed (very infrequently) by industrial robots: if you get in the way, they don't know to stop.
You've got to say, though, the finished product is very, very neat.
The first time I was exposed to the idea of a tattoo robot was in the 1997 movie Starship Troopers (made from Robert Heinlein's 1959 novel Starship Troopers). Heinlein does not describe a tattoo robot in the book.