An apparatus for verifying whether a user of an object is an authorized user of the object includes: (a) means for detecting a biometric feature of the user and generating data representing the biometric feature; and (b) a reader-printer for reading and printing on the object, which includes: (i) reader system for reading the object to obtain a digital representation of biometric information associated with the authorized user; and (ii) printer system for printing on the object; the apparatus being operable to cause the printer system to print on the object if the data matches the digital representation. Separately or incorporated into the apparatus, the reader-printer may include: (a) reader for reading the object to obtain a digital signature representing a unique feature of the object; and (b) printer for printing on the object if the digital signature matches a reference digital signature associated with the object.