I have precisely one tattoo, which I paid a trained artist an exorbitant amount of money to ink into my pasty skin. YouTuber Emily The Engineer may have developed a more cost-effective solution, however, as she's cracked open a 3D printer, bypassed its firmware, equipped it with a tattoo gun—and even found a willing volunteer to test it out.
Don't worry about the test subject's safety, though—there's a handy machine-halting panic lever installed for when they inevitably realise they've made a terrible mistake.
As Emily points out, she's printed a «ton of stuff» over the years, not least this world's largest Benchy boat attempt (via Hackaday).
However, «printing» on a human is a brave new frontier, and began with the merciless tearing apart of an old 3D printer frame capable of mapping out the X and Y axis of a 2D design.
Then began a process of convincing the printer to ignore things like temperature and medium variables, before a few 2D pen sketches were drawn on test paper and the back of Emily's hand.