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.

An authentication system includes an object including an authentication hologram disposed over an area of a surface of the object. The authentication hologram is defined by a pattern of reflective material and includes latent authentication information. The system includes a computer-readable medium including program instructions for execution by one or more processors. The program instructions are executable by the one or more processors to: (i) receive, from an image capture device, a digital image of the authentication hologram, wherein light reflected by the reflective material is captured in the digital image of the authentication hologram, and (ii) detect the latent authentication information in the digital image of the authentication hologram, wherein an effect of the reflected light is reduced to detect the latent authentication information.

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.

An authentication system includes an object including an authentication hologram disposed over an area of a surface of the object. The authentication hologram is defined by a pattern of reflective material and includes latent authentication information. The system includes a computer-readable medium including program instructions for execution by one or more processors. The program instructions are executable by the one or more processors to: (i) receive, from an image capture device, a digital image of the authentication hologram, wherein light reflected by the reflective material is captured in the digital image of the authentication hologram, and (ii) detect the latent authentication information in the digital image of the authentication hologram, wherein an effect of the reflected light is reduced to detect the latent authentication information.

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.

Systems, methods and technology for authenticating multi-layered objects using encoded signals such as digital watermarking. In one implementation, a value document includes a substrate and a removable overlayer, with a security feature comprising a digital watermark signal printed to cover portions of both the substrate and overlayer. The digital watermark signal includes spatially arranged signal elements forming a frame of reference. Tampering is detected by evaluating offset values associated with the signal elements, where misalignment within the frame of reference indicates tampering. In some implementations, the value document includes a first digital watermark on the substrate with synchronization and payload components, a token with a second digital watermark, and a removable sticker with a third digital watermark. Additional security features include split-mark configurations, tamper mark configurations, holographic foils with overprinted digital watermarks, and fragile tamper-deterrent features that deform upon tampering attempts, causing detectable signal distortion. Other combinations are also provided.