This chapter provides a brief overview of the different approaches to document authentication, before focusing on the different approaches to protection using elements sensitive to the variability inherent in copying systems. Improvements in the performance and availability of document printing and scanning systems have contributed to an upsurge in counterfeit document production. Printed document authentication processes rely on an initial registration step, carried out when the document is printed, before any verification can be carried out. A print test shapes (PTS) is a continuous element considered to be a binary object for analysis, containing the discriminating characteristics of a print. Copy-sensitive graphical codes (CSGCs) are discret elements that are designed to be difficult to duplicate from an authentic print. The performance of any document protection system based on the use of anti-copy elements, whether in the form of a PTS or CSGC, is dependent on in-depth knowledge of the print-scan chain involved.