I spent a couple of hours today experimenting with a color copying machine and my image editing program Gimp. The image below is the fruit of all my efforts:
Insert this png-image somewhere in a text document (like Word, Publisher, InDesign), decrease the absolute size of the image to exactly 8 x 8 milimeters. Print the document out in color. Then try to make a color copy of the page on a modern copying machine… Chances are you’ll be pretty surprised =)
The five yellow rings are part of a so called Counterfeit Deterrence System secretly introduced in the mid 90’s on bank notes world wide. When scanners and copying machines detect that precise pattern, size and color they are supposed to refuse their service.
The topic doesnt seem to be widely known (due to official secrecy) but its been dealt with for example by Nick Gessler.
But apart from my own suggestion above I haven’t seen anyone describing a practical procedure where you make use of the pattern yourself.