The Identification of Colour Photocopies AC ase Study by 30D6i7


									The Identification of Colour Photocopies
             A Case Study
   การจาแนกเครื่องถ่ ายเอกสารสี : 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
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
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
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
               Dotted patterns

counterfeit                  control specimens
                             (Rank Xerox Acolor 635 photocopier)

   consistent in terms of size and arrangement
      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

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