I have tried those suggestions before. I put it at an angle, covered less than and more than half and an assortment of other ideas. All to no avail. Researching it a bit discovered information is easy to find.

BUT, (Many) currency colors are protected/copyrighted so to speak and portions of designs are unique. I am guessing if a scanner 'sees' a certain percentage of color and/or a design in any orientation it stops. No doubt there are many other considerations.

My scanner will pull up the US Anti-counterfeiting website where the laws are spelled out. Even if I am within those limitations spelled out, my scanner will not scan. Luckily I have more than one scanner (older).

The software resides in the scanner. I remember reading about it in currency magazines well before I got a new scanner, and had forgotten about that tid-bit of information until I tried to scan a note. When the scanner says it won’t scan it….. it’s been the truth! I have been 100% Unsuccessful in scanning those notes. Fortunately, most notes scan fine. If the scanner turns me in, the FBI is pretty slow! I have had this scanner a long time. Besides, I would just blame Coco! (Chip stealing dog needs some jail time!)