See also: Photocopy Forgery
As in the case of typewritten documents, photocopied documents 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 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 a piece of 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.
Different makes of machines as well as different models within a manufacturer’s line may leave behind on the photocopy characteristics that are specific to that make and model such as grabber marks, paper edge depressions, designs incorporated into the paper, paper type, and toner type.
Paper is pulled through a photocopying machine by “grabbers.” Marks made by these grabbers are transferred to the paper. These may be in the form of small depressions at the edge of the paper, or areas of toner or tonerless spots on the finished photocopied document. Identification of designs incorporated into specialized paper for specific machines, paper type, and toner type in a questioned photocopy may additionally point to a specific make and model. Generally, however, machines requiring specialized paper have fallen into disuse and are rarely or never encountered.
Machine characteristics are noted and then searched through reference files. At times highly definitive opinions as to make and model are possible. This data base of reference material must continually be updated because of the short life of most photocopier models and the almost daily introduction of new models and technology. Unfortunately, because of the maintenance difficulty, few such reference collectins are in existence.
Obviously, if the questioned photocopy is a second, third, or more, generation removed from the original document, and if two or more different photocopy machines have been used in it’s lineage, the examination is more difficult and the definitiveness of the opinion is greatly lessened.
Photocopy to Photocopy Examination
Questioned photocopies may be examined visually for individual characteristic “trash” marks that may be made because of 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. As in photocopier identification, multiple generations of copies, the involvement of more than one photocopy machine, and machine maintenance, can severely 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 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.