This patent document discloses physical documents including metameric ink pairs. One claim recites 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 collective convey an encoded signal discernable from optical scan data representing at least a first portion of 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. Of course, other claims and combinations are described as well.

A concentric CRR sensor is claimed that is used as a form of currency verification in order to combat counterfeiting currency. The system comprises applying sets of concentric CRR printed with transparent conductive ink. In one embodiment, using the CRR as a passive RFID tag, changing the ring's radii, inner or outer, and in turn, created more encryption, and thereby prevents currency counterfeiting. In one or more embodiments, the serial number of the currency bill is used as a guideline to a selection algorithm to determine the size of the radii.

A concentric CRR sensor is claimed that is used as a form of currency verification in order to combat counterfeiting currency. The system comprises applying sets of concentric CRR printed with transparent conductive ink. In one embodiment, using the CRR as a passive RFID tag, changing the ring's radii, inner or outer, and in turn, created more encryption, and thereby prevents currency counterfeiting. In one or more embodiments, the serial number of the currency bill is used as a guideline to a selection algorithm to determine the size of the radii.

This patent document discloses physical documents including metameric ink pairs. One claim recites 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 collective convey an encoded signal discernable from optical scan data representing at least a first portion of 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. Of course, other claims and combinations are described as well.

The application discloses apparatus and systems for authenticating physical object, identification documents and security documents. Some such methods and apparatus involve signal encoding or digital watermarking.

The application discloses apparatus and systems for authenticating physical object, identification documents and security documents. Some such methods and apparatus involve signal encoding or digital watermarking.

The present disclosure relates generally to physical object authentication. In some embodiments, methods and apparatus relate to physical object authentication through comparison of randomly or pseudo-randomly occurring features with expected features. In some cases digital watermark or other indicia is used to convey the expected features. Of course, other combinations, embodiments and features are disclosed.

The application discloses printed objects including encoded information, and methods, apparatus and systems for authenticating such printed objects. Some such objects, methods and apparatus involve data hiding and/or encoded signals.