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

2. Outline Introduction The Proposed Method Experimental Results
Watermark Embedding
Hierarchical Tamper Detection
Tampered 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 blocks
X '=13× X mod 64 +1 4

5. Watermark Embedding (1/2)
avg_As=(I1+I2+I3+I4)/4 1 2 9 10 3 4 11 12 5 6 13 14 7 8 15 16 a1 a2 a3 a4 a5 a6 a7 a8 r
avg_Bs=(I1+I2+I3+I4)/4
Block A 1 2 9 10 3 4 11 12 5 6 13 14 7 8 15 16
avg_B=(I1+I2+…+I16)/16
Block B

6. Watermark Embedding (2/2)
Block A
num: # of 1s in the 6 MSBs of avg_Bs 69 78 82 97 35 46
210
102 51 33 73 44
173 83
145
126
avg_As=( )/4=57=( )2
r =
Block B
104 22 99
207 39 55 61
132 42 66 3 23
227
198
145
164
avg_Bs=( )/4=53=( )2
avg_B=( …+164)/16=97
v=0, p=1
104
104
Set 2LSBs to 0 1 1 22 22
104 20 96
204 36 52 60
132 40 64
224
196
144
164 39 39 55 54

7. Hierarchical Tamper Detection (1/3)
Level 1: for each sub-block B's of 2×2 pixels within block B' , verify v and p
avg_B’s=( )/4=53=
104 22 99
207 39 55 61
132 42 66 3 23
227
198
145
164
avg_B’=( …+164)/16=97
v'=0, p'=1
if v' is not equal to v
OR if p' is not equal to p
 This sub-Block is marked erroneous 1 1
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
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
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
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 1
valid
Block C
r = (00) = 56 = avg_Cs 69 78 82 97 35 46
210
102 51 33 73 44
173 83
145
126
avg_B’s=( )/4=55
valid
57= = =56
avg_B’s  avg_Cs
Block B’

10. Tampered Image Recovery
Mapping sequence: A  B
104 20 99
207 39 54 61
132 42 66 3 23
227
198
145
164 1
valid
Block B
r = (00) = 56 56 82 97
210
102 51 33 73 44
173 83
145
126 69 78 82 97 35 46
210
102 51 33 73 44
173 83
145
126
erroneous
Tamped Block A
Recovered Block A

11. 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.

19. 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. …