1. A method of determining whether an analog form of an object is an original analog form, the method comprising: comparing at least a portion of a digital recording made from the analog form, the analog form having an authentication pattern, with an original digital representation of the portion to determine a degree of dissimilarity between the recorded portion and the original digital representation of the portion; and using the degree of dissimilarity to determine whether the analog form is an original analog form; and performing a quality control of a printing process in dependence on the degree of dissimilarity; wherein the authentication pattern depends on a key and/or other information, the other information being displayed on the analog form.