A method of authenticating an object in which a computer system receives indicating data from a sensing device. The indicating data is generated in response to sensing of coded data provided on or in a surface associated with the object and is indicative of an identity of the object and at least part of a signature. The signature is in turn a digital signature of at least part of the identity. The computer system uses the indicating to determine a received identity and a received signature part, before using the using the received identity to determine at least a determined signature part. The determined signature part is then compared to the received signature part to authenticate the object.