Abstract: A method and apparatus for preventing reproduction of printed matter on a substrate by photocopying, telefaxing and the like. A substrate is provided with at least one main surface and a photochromic dye is applied to the one main surface, wherein the dye changes color in response to exposure to light with a response time which is a function of the amount of light absorbed by the dye in a given time period. The one main surface is illuminated with a given amount of light and the response time is decreased to accelerate the change in color of the dye by increasing the proportion of light which is absorbed by the dye from the given amount of light.

Abstract: A method and system for securing a substrate such as paper and the like against counterfeiting, photocopying, and facsimile transmission and an applicator and paper for use in the method and system and with the applicator. The method and system comprises providing a substrate having a background color on one surface thereof, covering at least one selected area of the surface with one of the colorless color developer and a colorless color former dye, wherein the color developer and color former dye react when mixed to produce a first given color which is different form the background color and applying the other of the colorless color developer and the colorless color former dye to at least a portion of the at least one selected area to change the background color to said first given color.