1. Ming-Shi Wang *, Wei-Che Chen 11 November 2006 present: 沈雅楓
A majority-voting based watermarking scheme for color image tamper detection and recovery
Ming-Shi Wang *, Wei-Che Chen
11 November 2006
present: 沈雅楓

2. Outline Introduction Proposed scheme Block-based watermark embedding
Watermark verification
Tampered image recovery
Experimental results
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3. Introduction
Two categories of conveying the authentication data: labeling-based schemes and watermarking based schemes.
The watermarking-based authentication scheme can be classified as either fragile watermarking, which is designed to detect any possible modification of the pixel values, or semi-fragile watermarking, which just distinguish content-preserving operations form malicious alteration.
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4. Proposed scheme
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5. Block division
M*M
Zij
8-bit R
8-bit B
8-bit G
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6. Example (Block mapping)
block Z1,1 k1=2, k2=3, M=10
So the recovery information of Z1,1 will hide in block Z2,1
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7. Block-based watermark embedding
In the proposed scheme, a
36-bit watermark consists
of the authentication data( 16 bits) and the recovery data( 20 bits) is embedded into the LSBs of each image block.
The authentication data of length 16 bits is obtained by exploiting both the local features of each image block and the global features of the image.
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8. Example (local feature)
the total number of 1s in the five MSBs of all the color
components of pixel l
The parity-check bit for pixel l: = = 1 = so =
The local feature of block Z1,1 :
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9. Example (global feature)
Hash function, MD5
………0
converted from 128 to 16 bits:
d0=d1||d2||…||d16=
the global features of image Z :
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10. Authentication data
Authentication =local (xor) global
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11. Example (recovery data)= = 1 =
(u,v) is mapped to (i,j)
That is because we just want 20
Bits for recovery data.
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12. Example (recovery data)
Assume Yu,v= , Cbu,v= Cru,v= ,(u,v) mapped to(1,1) So the recovery data in block Zi,j is: C1,1=
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13. Example(LSB embedding)
authentication data(16): recovery data(20):
R=……001
B=……101
G=……010
R=……101
B=……010
G=……100
R=……101
B=……101
G=……001
R=……101
B=……010
G=……011
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14. Watermark verification and Tampered image recovery
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15. Experimental results(1/3)
PSNR=37.96
PSNR=37.83
PSNR=37.96
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16. Experimental results(2/3)
Rtd=100%
Rtd=100%
Rtd=100%
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17. Experimental results(3/3)
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