1. An apparatus for deterring counterfeiting of documents having a characteristic color, the apparatus comprising: a detector adapted to detect look-up in a color look-up table of pixels having a color corresponding to the characteristic color, the pixels being part of a captured image to be printed; a counter adapted to count the number of detections in a page to be printed; and a modulator adapted to modulate the look-up value returned for the detected pixels, to thereby alter the characteristic color within the page to be printed.