A printing method and apparatus (100) for pre-exposing a digital watermark along a length of photosensitive medium at the time of manufacture is disclosed. The printing apparatus has an illumination source (60) for providing an exposure illumination, first and second LCD spatial light modulators (90a,...http://www.google.com/patents/US6930759?utm_source=gb-gplus-sharePatent US6930759 - Method and apparatus for exposing a latent watermark on film
