There is an art to applying tattoo ink. I was not aware that there is now a machine to apply tattoos. Can anyone provide a link to an image of such a machine?
Hollywood often requires certain realistic-appearing tattoos on their actors. Since these actors usually have a real life, somewhere away from the camera, they may want their "tattoos" removed after shooting "wraps." Dry transfer decals come to mind as a a way to accomplish this, but I am sure there are more "permanent" solutions that don't wash away under the rigors of acting. The decals, or whatever the "tattoos" were made from, should have an ink that is readily soluble in a common substance, such as cold cream, that allows for the "easy" removal of the tattoo.
I am in the process of inventing (just waiting for technology to catch up) a multi-color ink-jet spraying "paint brush" that has 3D positioning information built into the paint head, so it "knows where the head is" at all times. It remembers this positioning information too, so all the "artist" has to do is move this high-tech "paint brush" over the canvas and a stored image will be sprayed onto the canvas. It's smart enough to know what areas have received paint, and how much paint, so no skill is required to move the "paint brush" around and across the canvas.
This works great for painting scenes on the side of vans and tractor trailers, too, although it would be more efficient to just pull or roll these larger objects past a vertical array of paint spray nozzles. A variation on this theme appears in the Sci-Fi TV series "The Expanse," but I don't claim first discovery, or even believe an actual implementation could ever have an enforceable patent. Maybe someone here on EP will build it and make a ton of bux painting washable advertisements on tractor trailers. Professional truckers are washing their rigs anyway, so why shouldn't they pick up some advertising dollars as the roll down the highway?