mostly, the software in printers/scanners and Adobe's Photoshop alikes is looking out for the "EURion" pattern.

https://en.wikipedia.org/wiki/EURion_constellation

That is not to be confused with (dynamical) and non-visible tracking info on printed sheets, which in fact can have everything coded in. By that, even 1-bit printouts can be identified up to the source. If the printer model and #salt is printed alongside, the prosecution has evidence for the cases the printer involved.