Here’s the paper where they explain it. Basically, they make subtle fluctuations in layer height, adding or subtracting small amounts that are not visible to the naked eye, to encode 0s and 1s. So, maybe in principle this could run at the firmware level on your printer. Then, someone can use a microscope to read off the code from pieces of the printed part.
I would have some doubts about how reliable this is, given the relatively large tolerances in fdm printing, but they have a section about that in the paper, so I guess they at least have thought about it.
Fluctuations in layer height that are not visible? Dude, most printers are not even able to achieve a layer height consistency that would be invisible to the naked eye if they wanted to.
you know how easy it is to circumvent this?
relatively easy, its relatively easy. now you know.
