A method of determining a counterfeit security document which includes a number of coded data portions indicative of an identity of the security document; and at least part of a digital signature of at least part of the identity. The method includes using a sensing device to sense at least one coded data portion and generate indicating data. The indicating data is used by a processor to obtain a determined identity and at least one determined signature part, which are then used to determine if the security document is a counterfeit document.