Authenticating identification and security documents and other objects

A document comprising:

• a first surface;
• a second surface,
• in which the first surface comprises a first set of print structures and a second set of print structures, and in which the first set of print structures is provided on the first surface with a first ink, and the second set of print structures is provided on the first surface with a second, different ink, and in which the second, different ink comprise a metallic ink,
• in which the first set of print structures and the second set of print structures are positioned to obscure a location of the second set of print structures on the first surface,
• in which the second set of print structures is provided on the first surface in a pattern, the pattern yielding an energy signature upon excitation by a radio spectrum energy source, and in which the radio spectrum energy source emits in the range of 60-75 GHz.

A document comprising:

• a first surface;
• a second surface, in which the first surface comprises a first set of print structures and a second set of print structures,
• in which the first set of print structures and the second set of print structures collectively convey an encoded signal, in which an encoded signal is detectable from optical scan data representing the first surface,
• in which the first set of print structures is provided on the first surface with a first ink and the second set of print structures is provided on the first surface with a second, different ink, and
• in which the first ink and the second, different ink comprise a metameric pair, and in which the second set of print structures is provided on the first surface in a pattern, the pattern yielding an energy signature upon excitation by a radio spectrum energy source, and in which the radio spectrum energy source emits in the range of 60-75 GHz.