Optical Document Security

Optical document security has been used throughout history for good reason: the first line of defense against fraudulent documents is the clerk, whose eyes and brain are usually the most powerful pattern recognition system available. There has been a recent upsurge of interest in optical security technology, partly as a result of the new tools available to the counterfeiter (image scanners and color printers), partly as a result of flashy new optically variable devices for security, and partly as a result of increasing global security risks.

Rudolf van Renesse has created a book that is timely and valuable. In the preface, he begins with a question that comes right to the point: "Is document security a subject that should not be discussed in public?" Some of those he invited to contribute declined: "After mature reflection and consultation with various interested parties, we think that the result of such a publication could be counterproductive." Others saw the issue from the opposite standpoint: "The major strategic mistake one can make is underestimating the enemy. In the development of securities, oneshould take into account that possible counterfeiters can get information about the security elements with or without a book."

While the book naturally contains only contributions from the latter group, it does not fail to provide a broad and detailed overview of optical security technologies including photography, handwritten signatures, watermarks, microprinting, intaglio printing, colored fibers in currency paper, fluorescent inks, multilayer interference coatings, iridescent inks, retroreflective printing, embossing, diffusion transfer printing, luminescence, special chemistries, tamper sensitivity, liquid crystals, transparent overlays, serial numbering, modulated gratings, volume holograms, embossed holograms, kinoforms, grating dots, and zero-order gratings.

One of the most important chapters in the book is Chap. 2 by Dr. Ralph Tadema Wielandt, entitled "The evaluation of document fraud resistance." He gives an excellent answer to those who were invited but declined to contribute to the book: "In our opinion, only those security systems that still function adequately, even after all information and documentation is disclosed, are reliable." This sentiment is supported by a quote from K. J. Schell in the preface: " We would compare our strategy withthat of computer security, where the security of encrypting algorithms is based on keys, and not on the secrecy of the algorithms."

Dr. Wielandt presents a lucid analysis of document security systems as systems, as opposed to technologies. In his analysis the counterfeiter is as much a part of the security system as the security printer. Though the security printer and the counterfeiter are in different businesses, they are interdependent in all respects. They both have a systematic approach to reaching their goals. They are both powerfully motivated, and they both have substantial financial and technical resources. They are in a technology race constrained by risk, cost, time, and the capabilities of their opponents.

Though the cover of the book is decorated by a hologram and four of the seven samples included in the Appendix are holograms, there is not an undue emphasis on holography in the chapters . A novice to the field, and even some of the contributors themselves, would be well advised to read every chapter in this book. As van Renesse says, "The reader of this book will find that, almost invariably, the producers of one device tend to maintain that their device is superior to any other existing device and produce more or less convincing evidence of it. This can cause the reader some bewilderment." Reading only one selected chapter will give a reader a clear but almost certainly wrong impression of the value of a particular technology. However, van Renesse has done an admirable job of allowing the contributors to present their arguments without setting up a debate. A careful reader can sort through the information and opinions presented in this book and acquire a valuable overview of the challenge, process, and promise of optical document security.

One word of caution: most of the security devices presented can be counterfeited or effectively simulated. As pointed out by Dr. Wielandt, "It is generally agreed that a one hundred percent secure system does not exist and will never exist." None of the technologies alone can provide a high level of security against a determined and well-funded criminal organization. Only an intelligently designed and carefully tested security system, complete with constant re-evaluation and possibly including several of the available technologies, can reliably limit fraud to an acceptably low level. My personal hope is that the many users of optical document security will read this book and develop a new awareness of security as a dynamic system. A discerning reader will read the entire book, think about the wealth of methods described inthe chapters, then go back and read Chap. 2 again.