The problem is that images of $50 bills have enough alignment marks that the code to detect them could run on hardware from the ‘90s. From what I’ve seen, these bills naively assume that somehow the printer has to detect whether something is a gun or part of a gun. The fact that slicer software has to transform a mesh into gcode for a specific printer and specific settings means that a printer can’t just hash the file or something to check a blacklist. And how do you tell if something is part of a gun? A PVC pipe could be a gun barrel by that metric. Or maybe a trigger assembly is designed for a rubber band gun instead of an illegal firearm.
https://xkcd.com/1425/
I doubt there is a weapons expert that could look at a given STL file and unambiguously tell you whether something was “part of a gun” or not. If these laws pass, they will be either unenforceable, effectively ban all 3D printer sales due to the immense difficulty of compliance, or worse, be another avenue for selective enforcement.
Furthermore, the whole “ghost guns” thing is entirely overblown and misunderstood by people who have never seen or used a 3D printer except in the movies, where Hollywood has latched onto the idea that they are designed primarily for making guns. A consumer grade 3D printer is going to print a gun that will explode in your hands the first time you try to use it, if any of the meaningful parts of the gun are printed. And nothing is stopping people from say, fabricating gun stocks with a table saw and router, or building a gun out of hardware store parts. Why aren’t we also banning mills and lathes while we’re at it? There are also chemicals at a hardware store that could be used to make explosives. If the concern was really “making guns at home”, we’d outlaw Ace Hardware and Home Depot.