Patent ID: 6301363
Filing Date: 2001-10-09
Classification: G07D

Abstract:
A system for viewing a subtle image on a security document comprising:a security document comprising a subtle image formed on a first face of said document, whereinsaid subtle image is formed by a set of security image elements and a set of complementary security image elements,one of said set of security image elements and said set of complementary security image elements is not readily duplicated by a photocopier at a predetermined photocopier setting, while the other of said set of security image elements and said set of complementary security image elements is readily duplicated by said photocopier at said predetermined photocopier setting,said security image elements are arranged in a security image element array characterized by a first element array frequency f.sub.1, andsaid complementary security image elements are arranged in a complementary security image element array characterized by a second element array frequency f.sub.2 ;a document viewer comprising a plurality of lens elements arranged in a lens element array, wherein said plurality of lens elements define a document viewer focal plane, and said lens element array is characterized by a lens element array frequency f.sub.0, where f.sub.0, f.sub.1, and f.sub.2 satisfy at least one of the following document characteristic equationsf.sub.1.ident.af.sub.0f.sub.2.ident.bf.sub.0f.sub.0.ident.cf.sub.1f.sub.0.ident.df.sub.2where a, b, c, and d are positive whole numbers and where a.notident.b and c.notident.d; anda document receiving station positioned to receive said document such that said document may be positioned substantially in said document viewer focal plane.