666 () ? B O O M ! ? posted 2 years ago by TheQStrategy 2 years ago by TheQStrategy +671 / -5 172 comments share 172 comments share save hide report block hide replies
My guess it wouldn't be an ordinary black light, but a specific frequency which can only reveal images.
Here is another post about watermarks disguised as random dots.
All modern printers already give out watermarks so you can track which printer the paper came from and on what date.
Machine identification code