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. 2519-2529

Outline Introduction The Proposed Method Experimental Results Watermark Embedding Hierarchical Tamper Detection Tampered Image Recovery Experimental Results Conclusions Comments

Introduction Watermarking Method for Image Tamper Detection and Recovery

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

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

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=(69+78+35+46)/4=57=(00111001)2 r = 001110 Block B 104 22 99 207 39 55 61 132 42 66 3 23 227 198 145 164 avg_Bs=(104+20+36+52)/4=53=(00110101)2 avg_B=(104+20+96+204+…+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

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=(104+20+36+52)/4=53=00110101 104 22 99 207 39 55 61 132 42 66 3 23 227 198 145 164 avg_B’=(104+20+96+204+…+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

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.

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 = 001110(00) = 56 = avg_Cs 69 78 82 97 35 46 210 102 51 33 73 44 173 83 145 126 avg_B’s=(68+76+32+44)/4=55 valid 57=00111001=00111000=56 avg_B’s  avg_Cs Block B’

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 = 001110(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

Experimental Results (1/7)

Experimental Results (2/7)

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).

Experimental Results (4/7)

Experimental Results (5/7)

Experimental Results (6/7)

Experimental Results (7/7)

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.

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. …