the identification of colour photocopies a case study...

The Identification of Colour Photocopies

A Case Study การจำ�าแนกเคร�องถ่�ายเอกสารส� :

กรณี�ศึ�กษา

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

เคร�อง 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