Right. I think photocopiers are somewhat aggressive in their money detecting algorithms. I remember someone having a problem photocopying something that was obviously (to a human) not real currency. It wasn't even prop currency which is supposed to look real on camera. This was something for a game or a party or something.

I think the algorithms have to be a bit loose for the currency detection because there are new bills that are released, and many photocopiers aren't constantly connected to the Internet, and may not have the newest firmware.

But, for a gun, that's going to be a much harder matching problem, especially because it's a 3d object and after the print the user could snip things off or glue things together. Plus there's the constant remixing of 3d printed things where someone improves on a design and posts it and people adopt then adapt the new design. The only realistic way for it to work is for the printer to do some complex finite element analysis or something on everything anybody tried to print to see if maybe it could perform the function of a certain part of a gun. And that's absurd because that's something you need a workstation class PC to even consider doing, while 3d printers use chips that are... let's just say they can't run Doom.