Patent ID: 8289535

Claim:
A method of using a mobile device to authenticate a print medium online before completing printing onto the print medium, the mobile device including processing means, a printhead, a sensor in a print path of the printhead, a transmitter and a receiver, the print medium comprising a laminar substrate, the method comprising steps of: using the sensor to sense a plurality of coded data portions provided on a surface of the substrate while the substrate moves past the sensor in the print path, each coded data portion encoding: an identity of the print medium; and part of a signature, the signature being a digital signature of at least part of the identity; using the processing means to determine, from the sensed coded data: the identity of the print medium; and a plurality of signature parts from respective coded data portions; using the transmitter to send first data to a remote computer system, the first data being indicative of the identity, and the parts of the signature; using the receiver to receive second data from the remote computer system in reply to the first data, the second data being indicative of whether the print medium is authentic based on the identity and the parts of the signature; and in the event the print medium is authentic, using the printhead to print onto the print medium.