Plural color anti-copying systems for xerographic and electrostatic copying machines

An anti-copying method of preparing an original, image-bearing paper document to inhibit or prevent intelligible reproduction of the image on the original document with xerographic and electrostatic copying machines, comprising the steps of providing said document with a yellow background, printing a first pre-selected portion of said image on said background in a first pre-selected color having a dominant wavelength which is greater than that of said yellow background, and printing a second pre-selected portion of said image in a second pre-selected color having a dominant wavelength which is less than that of said yellow background, said first and second pre-selected portions being selected in such a way that failure to intelligibly reproduce either one of said first and second portions renders the image as a whole at least generally incomprehensible.

The anti-copying method defined in claim 2 or 5 wherein said second color is yellow-green.

The anti-copying system defined in claim 2 or 5 wherein said second color has a dominant wavelength in the range extending from about 550 nanometers to about 565 namometers.