The Identification of Colour Photocopies A Case Study การจำแนกเครื่องถ่ายเอกสารสี : กรณีศึกษา C.K Li and S.C. Leung Forensic Science Division, Government Laboratory, Ho Man Tin Government Offices,88,Chung Hau Street,Ho Man Tin, Kowloon, Hong Kong

Introduction The photocopy machine has essential Office equipment in modern times. The high quality of reproduction of document has resulted in a more extensive usage of colour photocopying

Photocopy

Case : counterfeit Hong Kong ( a Rank Xerox A- colour 635 photocopier ) Examination : microscopic counterfeit repeated dotted patterns to identify the colour photocopier

Method and Materials Dotted patterns on colour photocopies : Series of repeated patterns of yellow dots - model the photocopying machine - to identify

Figure1 three images of Hong Kong $500 on A4 paper

The yellow dots were too pale to be clearly seen the naked eye / a hand lens used VSC : patterns on counterfeit with blue light and filter at 610 nm

เครื่อง VSC

Figure 2 illustrates one complete unit of the patterns as visualized in the monitor of the VSC

Results and Discussion Suspected : a Rank Xerox A color 635 photocopier printing the counterfeit. Specimens : sheets of control prepared with this photocopier

Dotted patterns : electronic devices in the machine during the photocopying process Ques : patterns unique, utilized to prove that photocopying was produce the counterfeit ? Ans : survey was colour photocopies by machines commonly available in Hong Kong

Survey on colour photocopies Table1. A summary of a survey on the presence of regular dotted patterns on colour photocopies made by Rank Xerox,Canon and Ricoh photocopierss

Figure 3. Arrangements of the dotted marks Depicted in sample Photocopies from three of photocopying machine

Figure 4. Arrangement of repeated dotted motifs present on a photocopy as visualized in the monitor of the VSC

Figure 5. Example of the dotted motifs depicted from Cannon colour copiers

Conclusion Dotted patterns counterfeit control specimens (Rank Xerox Acolor 635 photocopier) consistent in terms of size and arrangement

patterns  serial numbers machines  identifying the photocopiers (arrangements of the dots in the 8x15 grid unit cells.)

Results from the survey ‘identification marks’ on the photocopies are unique for a particular copying machine. : Xerox(Hong Kong) Ltd. Patterns of dots represent the serial numbers that identify : Canon CLC350, CLC700 and CLC800 colour copiers also serve as identification codes

Q & A