the identification of colour photocopies a case study...
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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