See also: Photocopy Forgery
In the recent past, most business offices contained only specialized job-specific office machines, such as photocopiers, facsimile machines, printers, and scanners. While this is still the norm in many modern offices, many offices now employ multi-purpose machines that combine all, or many combinations of machines. These are produced by many manufacturers in a myriad of models. Causing further confusion for the document examiner, these specialized and multi-purpose machine continue to evolve on what seems to be a daily basis.
Documents photocopied on straight photocopiers and multi-purpose machines may contain may contain elements likely to identify the source of the original document, the model machine that was employed in its manufacture, or the specific machine if one has been identified.
Most modern day photocopying machines operate in a more or less similar fashion. The image of the document to be copied is captured by camera lens and transferred to a cylindrical drum usually coated with a light sensitive substance such as selenium. This drum has been charged with a static electric charge which dissipates when exposed to light. The image of the document transferred to the drum is made of up of light and dark areas that will create similar or corresponding areas of more, or less, static electric charge on the drum. The drum is then, in turn, bathed with toner. This may be either in a dry or wet form depending upon the specific machine. Toner has an inherent affinity for static electricity and consequently clings to those areas of the drum in quantities proportional to the electrostatic charge. This toner in turn is transferred to the receiving paper that will then be subjected to a fixing process, usually in the form of heat, which fuses and attaches the toner to the paper.
At one time, different makes of machines as well as different models within a manufacturer’s line left behind, on the photocopy, characteristics that were specific to that make and model such as grabber marks, paper edge depressions, designs incorporated into the paper, and/or used specialized papers, and toner types.
Machine characteristics were noted and then searched through reference files. At times highly definitive opinions as to make and model were possible. This data base of reference material had to be continually be updated due of the short life of most photocopier models and the almost daily introduction of new models and technology. Unfortunately, because of the reference maintenance difficulty, few such reference collections are in existence and newer technology has for the most part obviated their use.
In place now, is a counterfeit protection system (CPS) that is currently employed by many, but not all, photocopy machine manufacturers. These CPS codes can link two or more photocopied documents as having been produced by the same machine. Unfortunately, the CPS database is not available for public consumption and the decoding information classified. Further, just the process to find the code on a photocopied document is not simplistic and can require highly specialized equipment, such as a video-spectral comparator (VSC).
Photocopy to Photocopy Examination
While the CPS is not readily available, questioned photocopies may be examined visually for individual characteristic “trash” marks that may be occasioned by dirt, scratches, and other extraneous marks on the surfaces of the drum, cover, glass plate, or camera lens of a photocopy machine. A comparison of these marks on a questioned document with those marks made by a specific machine may serve to identify or eliminate that particular machine as the source of the document in question. Similarly, a side-by-side comparison of two or more questioned photocopies may reveal if they are the product of a common photocopy machine. Multiple generations of copies, the involvement of more than one photocopy machine, and machine maintenance, can limit the conclusiveness of the resultant opinions.
Because of the usually large physical size of many photocopiers, it is often impractical to transport the machine to the laboratory. When this is the case, the submitter can simply run sheets of plain paper through the photocopier and submit those “standards” to the laboratory. It should be noted that the photosensitive drum of some machines may copy three or more sheets of paper before it has made a complete revolution. For this reason, it is advisable to run at least ten sheets of paper through each suspect machine. These “specimens” should be kept in the order that the machine produced them.