The present invention provides methods and systems to authenticate identification documents. In a first implementation, an identification document includes a photograph and a digital watermark. The digital watermark carries first facial recognition data corresponding to a face depicted in the photograph. Optical scan data representing the photograph is received, and a second facial recognition data is derived. The first facial recognition data is recovered from the digital watermark, and is compared with the second facial recognition data.

 
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> Controlling an RFID reader by observing a change in inductance

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