# Robust Visual Cryptography-based Watermarking Scheme for Multiple

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```							                       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

2
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

4
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

5
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

6
2012/5/24
cover image
INTRODUCTION (5/5)

7
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

10
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

11
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)

17
CONCLUSIONS

• VC-based watermarking scheme:
• Has strong robustness

• Satisfies imperceptibility

• Satisfies the blindness

• Gains security properties

18

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