Robust Visual Cryptography-based Watermarking Scheme for Multiple

							                       Robust Visual Cryptography-based
                       Watermarking Scheme for Multiple
                       Cover Images and Multiple Owners

Source:      IET Information Security, Vol. 5, Iss. 2, pp. 121–128, 2011
Authors:     F. Liu and C-K Wu
Presenter:   Huynh Ngoc Tu
Date:        Sept. 28th , 2011
                    OUTLINE

• INTRODUCTION
  • Introduce some related techniques

• THE PROPOSED SCHEME

• EXPERIMENTAL RESUTLS

• CONCLUSIONS



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                      INTRODUCTION (1/5)

 Watermarking: Technique to protect the copyright of digital media

                   (image, text, music and movie)

Criteria:
     Imperceptibility: the watermarked images are identical/indistinguishable to
      the original cover images

     Robustness: the watermark still can be extracted even the watermarked

       image suffered from various attacks

     Security

     Blindness

                                                                              3
                      INTRODUCTION (2/5)

 Visual cryptography (VC)
    Share a secret into n parts and distribute to n participants

    Any k of n shares can recover the secret image

    Any less than k shares cannot obtain any information of the secret image



                           Apply this technique to protect the
                          owners’ copyrights of the cover image




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                    INTRODUCTION (3/5)
          Arnold’s cat map

 xn 1  1     a   xn             xn 
                  y  mod N  A  y  mod N
 yn 1  b ab  1  n              n
a, b : intergers and det( A)  1




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                          INTRODUCTION (4/5)
            DWT Transformation                         LL                                 HL
255 255 154 156 155 152 152 154
                                                255     153.5      154    151.25    0           -1    0.5     1.25
255 255 151 153 154 155 153 146
                                                154     154       152.75 153.25     -1          0     0.75    0.25
153 155 154 154 154 152 153 152
                                               154.25 152.75 151.75 153.25         0.75     -0.75     0.75    -1.25
153 155 154 154 153 152 154 154
155 154 153 153 152 151 152 153
                                   one-level    153     153        153    158.25    0           -1    0.5     -6.5
                                                 0          1.5    -0.5    1.75     0           0      1      -2.25
155 153 151 154 153 151 152 156    DWT           0          0      0.25   -0.75     0           0     0.25    0.25
153 152 150 153 154 153 152 151
                                                0.25    0.25      -0.25   -0.75    -0.25       0.75   -0.25   0.75
153 154 154 155 153 152 152 178                 -0.5    -1.5       0.5    -6.75     0.5        -0.5    0       7
 Cover image (8×8)                                     LH                                  HH



                                  one-level
                                  HDWT

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                                                                                                        2012/5/24
          cover image
INTRODUCTION (5/5)




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             EMBEDDING ALGORITHM

         Step 1                Step 2




                                                   Step 6


         Step 3                Step 4


Step 5




                  The flowchart of the embedding algorithm   8
                  EXTRACTING ALGORITHM

         Step 1             Step 2
                                                          Step 5



                                              Step 4                Step 6



Step 3
                                                           Step 7




                   The flowchart of the extracting algorithm         9
          EXPERIMENTAL RESULTS (1/8)




Cover image    Watermark             Key image          Secret share




                 Test images for the first simulation

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             EXPERIMENTAL RESULTS (2/8)




(a) and (b) Cover images   (c) Watermark         (d) and (e) Key images   (f) Secret share


                    Test images for the second simulation




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EXPERIMENTAL RESULTS (3/8)




                                                   12
  Attacked images and their extracted watermarks
EXPERIMENTAL RESULTS (4/8)




  Attacked images and their extracted watermarks   13
EXPERIMENTAL RESULTS (5/8)
EXPERIMENTAL RESULTS (6/8)




Average accuracy ratio values for attacks a1, . . ., a10 for
                the third simulation
                                                               15
EXPERIMENTAL RESULTS (7/8)




                             16
EXPERIMENTAL RESULTS (8/8)




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                        CONCLUSIONS

• VC-based watermarking scheme:
   • Has strong robustness

   • Satisfies imperceptibility

   • Satisfies the blindness

   • Gains security properties




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