Fax machine, copier, and printer analysis
Fax machine, copier, and printer analysis refers to the examination of the output produced by these devices to establish the origins and authenticity of printed documents. This analysis plays a crucial role in legal contexts, particularly in cases involving document authentication, where suspected forgery is a concern, and document tracing, which often arises in serious criminal cases such as extortion and terrorism. Though seemingly similar at a glance, different types of printers and copiers generate distinct physical and chemical characteristics that forensic experts can identify. These characteristics can include variations in print clarity, marks from malfunctioning machinery, and the absence of traditional typewriter erasures.
Advanced analytical techniques, such as scanning electron microscopy and chemical spectrometry, allow forensic specialists to examine inks and toners at a molecular level. They can discern unique "electronic signatures" from printer outputs and match them to specific brands and models, aiding in the investigation of criminal activity. As technology evolves, so do the techniques used by forensic examiners, ensuring they remain effective against increasingly sophisticated methods of document forgery and manipulation. This field not only aids in criminal investigations but also plays a vital role in maintaining the integrity of legal documents in various contexts.
Fax machine, copier, and printer analysis
DEFINITION: Examination of output from ink-jet and laser computer printers, electrostatic copiers, and fax machines to determine the origins or authenticity of printed documents.
SIGNIFICANCE: Printer and copier analysis based on output is useful in two broad classes of cases: document authentication (generally in cases of suspected forgery), where the main aim is to demonstrate that a document could not have come from a specific source, and document tracing, where the aim is to connect an item with a specific printer and time frame. The latter is considerably more difficult. Document tracing is most likely to arise in criminal cases involving ransom notes, extortion, or blackmail. It may also provide key evidence in terrorism and espionage investigations.
Since the mid-1980s, high proportions of documents relevant to civil and criminal cases have been produced by fax machines, photocopiers, and printers connected to computers. Although they may appear indistinguishable under casual inspection, such documents have physical and chemical characteristics that enable forensic examiners to identify the equipment used to produce the pages and the approximate time frame in which they were generated. The techniques used rely on the extremely rapid rate of change in the printer industry and require sophisticated equipment linked to computer programs capable of discerning subtle differences in the patterns of complex digital signals.
Magnification
Examination under low magnification is usually sufficient to allow analysts to distinguish the outputs of different classes of printers. Ink-jet printers produce more blurred outlines than do laser printers and toner-based photocopiers. Older single-element printers leave indentations on the sheets of paper that pass through them that are similar to those made by electric typewriters. Also, paper may be marked by damaged or improperly aligned feeding machinery in printers. Incidental marks associated with dirty glass can originate either at input (scanner/fax) or at the time of printing. Printer output of any description can be distinguished from typewritten originals by the complete absence of erasures and strikeovers.
In an authentication case, the key question is usually whether two documents were produced on the same equipment. For example, if a questioned contract, originally filled in by typewriter on a printed form, contains substituted pages made by a forger who has scanned the originals, made changes to the text electronically, and printed the altered pages on a laser printer, the differences between original typewritten copy and the scanned would be evident on close examination. If visual inspection under low magnification fails to detect any useful information on a questioned document, analysts may apply a wide array of more sophisticated techniques, such as those described below, but unless large sums of money are involved or the case is politically charged, these are seldom employed.
Electronic and Chemical Analysis Methods
When low-volume laser and ink-jet printers and copiers first hit the mass market, forensic specialists assumed that this would make tracing documents to individual printers virtually impossible. In fact, every brand and model of printer (including photocopiers that scan input prior to printing) has a distinctive electronic signature that can be “read” from the output using a scanner and appropriate software. One brand of higher-end color copier invisibly attaches the serial number of the machine to copies, a practice that may well expand. Computer analysis can also reveal banding and other flaws resulting from machine malfunction.
The most powerful tools for tracing printer and copier output, however, rely on the chemical compositions of dyes and toners, both the pigments themselves and the compounds used to bind them to the paper. The exact formulation of each dye and toner is specific not only to the manufacturer but also to a narrow timeframe, measured in months.
Different tools provide analysts with complementary information. Scanning electron microscopy (SEM) produces a high-resolution image of surface features, including the drying patterns of inks. As an adjunct to SEM, energy-dispersive spectroscopy (EDS; also known as energy-dispersive X-ray spectroscopy, or EDX) measures the X-ray emission spectra of compounds bombarded by electrons. An EDS reading indicates which atomic elements are present in a sample and in what proportions. X-ray fluorescence spectroscopy detects the presence of certain compounds based on the visible or they emit when bombarded by X-rays.
Infrared absorption spectrometry detects specific types of chemical bonds in organic molecules. This technique is useful for distinguishing between chemically similar bonding agents. Thin-layer and pyrolysis depend on the rate of diffusion of compounds and are useful for distinguishing mixtures of complex organic chemicals, such as those in dye-based inks.
All of these spectrographic and chromatographic methods require extensive costly equipment, most of it, however, not specific to forensic science. Most techniques involve sample destruction, but only very small amounts of material are required. After a reading is obtained, the examiner uses a computer program to compare that reading either to a sample of known origin or to a library of chemical signatures. Such libraries are maintained both by leading national forensic laboratories and by toner and ink manufacturers.
One California investigation into and insider trading focused on a company executive who denied ever having seen a certain set of privileged documents. By analyzing ink and printer characteristics, forensic scientists were able to demonstrate with a high degree of probability that the papers in question were printed on the executive’s home computer system.
Chemical analysis of inks and toners does not even require intact documents. In a 2006 Japanese investigation, the burned critical documents. Scientists were able to analyze the toner found on the charred fragments and ashes; it matched that of the blackmail letters, strengthening the prosecution’s case.
The most persistent and organized criminals will undoubtedly become more adept at circumventing techniques now in place for detecting fraudulent and extortionist uses of printers and photocopiers. Forensic document examiners must, thus, stay abreast of the rapidly evolving technology in this area.
Bibliography
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