A Hierarchical Digital Watermarking Method for Image Tamper Detection and Recovery

Phen-Lan Lin, Chung-Kai Hsieh, and Po-Whei Huang

Pattern Recognition

Vol. 38, Issue 11, December 2005, pp. 2519-2529

2

Outline Introduction The Proposed Method

Watermark EmbeddingHierarchical Tamper DetectionTampered Image Recovery

Experimental Results Conclusions Comments

3

Introduction

Watermarking Method for Image Tamper Detection and Recovery

4

Block mapping sequence generation algorithm (4 ×4 pixels/block)

1-1 mapping : X ' = [ f ( X ) = ( k × X ) mod N ] + 1, • X , X ' are the block number ( [0, ∈ N− 1 ])• k is a secret key, (a prime and ∈ Z − {N 's factors }) • N is the total number of blocks in the image

The original block The mapping of blocksX '=13× X mod 64 +1

5

Watermark Embedding (1/2)

1 2 9 10

3 4 11 12

5 6 13 14

7 8 15 16

1 2 9 10

3 4 11 12

5 6 13 14

7 8 15 16

avg_B=(I1+I2+…+I16)/16

avg_Bs=(I1+I2+I3+I4)/4

Block B

Block A

avg_As=(I1+I2+I3+I4)/4

a1 a2 a3 a4 a5 a6 a7 a8

r

6

Watermark Embedding (2/2)

69 78 82 97

35 46 210 102

51 33 73 44

173 83 145 126

104 20 96 204

36 52 60 132

40 64 0 20

224 196 144 164

0 1 1 0 1 0

0 0 0 1 0 1

0 0 1 0 0 1

0 0 1 1 0 1

Block A

Block B

avg_As=(69+78+35+46)/4=57=(00111001)2

avg_Bs=(104+20+36+52)/4=53=(00110101)2avg_B=(104+20+96+204+…+164)/16=97

r = 001110

v=0, p=1

104

22

39

55

0 0

1 0

1 1

1 0

104

22

39

54

104 22 99 207

39 55 61 132

42 66 3 23

227 198 145 164

Set 2LSBs to 0

num: # of 1s in the 6 MSBs of avg_Bs

7

Hierarchical Tamper Detection (1/3)

104 22 99 207

39 55 61 132

42 66 3 23

227 198 145 164

Level 1: for each sub-block B's of 2×2 pixels within block B' , verify v and p

avg_B’s=(104+20+36+52)/4=53=00110101

avg_B’=(104+20+96+204+…+164)/16=97

v=0, p=1

0 1 1 0 1 0

0 0 0 1 0 1

0 0 1 0 0 1

0 0 1 1 0 1

0 0

1 0

1 1

1 0

if v' is not equal to v OR if p' is not equal to p This sub-Block is marked erroneous

v'=0, p'=1

After Level 1 detection, each sub-block is marked valid of erroneous

8

Hierarchical Tamper Detection (2/3)Level 2: For each block of size 4 × 4 pixels, mark this block erroneous if any of its sub-block is marked erroneous; otherwise, mark it valid.

104 22 99 207

39 55 61 132

42 66 3 23

227 198 145 164

Level 3: For each valid block of size 4×4 pixels, mark the block erroneous if there are five or more erroneous blocks in its 3×3 block-neighborhood,

Error B Error

Error Error Error

104 22 99 207

39 55 61 132

42 66 3 23

227 198 145 164

After Level 2 detection, each block is marked valid of erroneous

Most surrounding blocks of some valid block are erroneous, this block hardly remains valid.

9

Hierarchical Tamper Detection (3/3)

Level 4: only required for resisting against VQ attack, assume mapping sequence: B C

104 20 99 207

39 54 61 132

42 66 3 23

227 198 145 164

0 1 1 0 1 0 0 0

0 0 0 1 0 1 0 0

0 0 1 0 0 1 1 1

0 0 1 1 0 1 1 0

r = 001110(00) = 56 = avg_Cs

Block C

69 78 82 97

35 46 210 102

51 33 73 44

173 83 145 126

Block B’

avg_B’s=(68+76+32+44)/4=55

avg_B’s avg_Cs

57=00111001=00111000=56

valid

valid

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Tampered Image Recovery

69 78 82 97

35 46 210 102

51 33 73 44

173 83 145 126

104 20 99 207

39 54 61 132

42 66 3 23

227 198 145 164

0 1 1 0 1 0 0 0

0 0 0 1 0 1 0 0

0 0 1 0 0 1 1 1

0 0 1 1 0 1 1 0

Block B

56 56 82 97

56 56 210 102

51 33 73 44

173 83 145 126

r = 001110(00) = 56

Tamped Block A Recovered Block A

valid

erroneous

Mapping sequence: A B

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Experimental Results (1/7)

12

Experimental Results (2/7)

13

Experimental Results (3/7)

• M1: Covering the whole image with leaf patterns, as depicted in Fig. 8(b).

• M2: Covering the whole image with another image, as depicted in Fig. 8(c).

• M3: Covering the whole image with fruit patterns, as depicted in Fig. 8(d).

• M4: Spreading plenty of mist to the whole image, as depicted in Fig. 8(e).

14

Experimental Results (4/7)

15

Experimental Results (5/7)

16

Experimental Results (6/7)

17

Experimental Results (7/7)

18

Conclusions

A hierarchical digital watermarking scheme for image tamper detection and restoration is proposed.

The proposed method uses parity check and intensity comparison with 3-Level detection for tamper detection.

The proposed method uses 2-LSBs of each pixel to restore the check bits and restore information.

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Comments

Level 4 detection resists against VQ attack (collage attack)

Something is wrong with Level 4 detection Reversible watermarking such as DE or

histogram shifting is not suitable for tamper detection and recovery, this is because the bit-rate is low.

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