1. Huijuan Yang, Alex C. Kot, IEEE Fellow IEEE Transactions on Multimedia, Vol. 9, No. 3, Apr. 2007 Multimedia Security Final Project R97922062 葉容瑜 R97922003 程瀚平

2.  Introduction  Proposed Method  The Authentication Mechanism  Experimental Results  Conclusions

3. Introduction(1/3)  Digital documents Ex. certificates, digital books, fax, personal documents  How to ensure the authenticity and integrity of digital documents, as well as detection of tampering and forgery, become a serious concern  Powerful image editing software  Data hiding for binary images authentication has been a promising approach to alleviate these concerns

4. Introduction(2/3)  Data hiding on binary images can be done the lower level: flipping pixels from black to white and vice versa the higher level: modifying width of strokes and spacings between characters and words  In this paper, our focus is on data hiding for binary images in lower level for the purpose of image authentication

5. Introduction(3/3)  Define a “connectivity-preserving” criterion to assess the “flippability” of a pixel  Connectivity among pixels plays an important role to their visual qualities Wu et al.’s approachProposed approach Visual distortion Connectivity Smoothness 4-connectivity 8-connectivity Uneven embeddability of the image Shuffling Embeddable blocks/ Embeddable pixels (cryptographic signature)

6. The Main Objectives 1. Assess the “flippability” of a pixel using the connectivity- preserving criterion to achieve good visual quality of the watermarked image 2. Handle the “uneven embeddability” of the image by adaptively embedding the watermark only in those “embeddable” blocks 3. Study the invariant features in flipping pixels in binary images to achieve blind watermark extraction 4. Explore different ways of partitioning the image to achieve larger capacity 5. Investigate on how to locate the “embeddable” pixels in the watermarked image so as to incorporate cryptographic signature to achieve higher security

7.  Introduction  Background  Proposed Method  The Authentication Mechanism  Experimental Results  Conclusions

8. Background 1. How to choose suitable pixels to carry the watermark data so that the visual distortion is low 2. How to handle the “uneven embeddability” of the host image such that the “flippable” pixels can be efficiently used 3. How to utilize the invariant features in the data embedding process to extract watermark without requiring the presence of original image (blind) 4. How to increase the capacity by partitioning the image in appropriate ways 5. How to locate the “embeddable” pixels in order to incorporate cryptographic signature to ensure authenticity and integrity of the watermarked images

9.  Introduction  Proposed Method Flippability Decision Block Partition Embeddability Capacities Watermark Embedding and Extraction  The Authentication Mechanism  Experimental Results  Conclusions

10. Flippability Decision  Flippability The transitions from the pixel to its eight neighbors in a 3 * 3 block In particular, the 4- and 8-connectivity among pixels VH Transition IR Transition C Transition

11. VH Transition  N vw : the number of uniform white transitions along vertical and horizontal directions  N vb : the number of uniform black transitions along vertical and horizontal directions Black: 1 White: 0 N vw = 0, N vb = 2 => N vw = 0, N vb = 0 N vw = 0, N vb = 0 => N vw = 0, N vb = 0

12. IR Transition  N ir : the number of the interior right angle transitions Black: 1 White: 0 N ir = 0 => N ir = 1 N ir = 0 => N ir = 0

13. C Transition  N c : the number of transitions from the center pixel to the sharp corners Black: 1 White: 0 N c = 1 => N c = 0 N c = 0 => N c = 0

14. Flippability/Connectivity-Preserving Criterion  Flippable VH transition, IR transition, and C transition remain the same before and after flipping the center pixel  Flip the pixel will not Destroy the connectivity b/w pixels in the neighborhood(VH) Create extra clusters as well(IR) Destroy the 8-connectivity among pixels(C)  By satisfying the “Connectivity-Preserving” criterion, the local connectivity is preserved

15. Block Partition  Several different types of blocks Fixed 3*3 block (FB) Non-interlaced block (NIB) Interlaced block (IB)

16. Embeddability  Determined pixels Non-interlaced block scheme: all pixels except the boundary pixels Interlaced block scheme: all pixels except those lie in the sharing rows and columns  The embeddability of a block depends on the “flippability” of the determined pixels in the block

17. Capacities  Only one pixel is flipped in each block => The prob. of a pixel to be “flippable” in a block is independent to other pixels  Assume the probability that a pixel satisfies the “Flippability Criterion” is p FB: The prob. of each block to be “embeddable” is p NIB: The prob. is 1 – (1-p)^(n-2) 2 IB: The prob. is 1 – (1-p)^(n-2) 2  A larger block size definitely will increase the prob.for a block to be “embeddable”, however, the total number of blocks will be decreased => Decrease the capacities

18. Watermark Embedding 1. Partition the image into equal size square blocks, note that the block size does not need to be square 2. Determine the flippability of the determined pixels based on the “Flippability Criterion” 3. Once a pixel is identified as “flippable”, the block is marked as “embeddable”. The current “flippable” pixel is identified as the “embeddable” pixel, i.e., “embeddable” location of the block 4. Proceed to the next block 5. Repeat steps 2 to 4 until all the blocks are processed 6. Embed the watermark in the “embeddable” blocks by flipping the “embeddable” pixels (if needed) to enforce the odd-even feature of the number of black or white pixels in the block

19.  Embeddable pixels = flippable pixels  Flipping a pixel in a block may affect the “flippability” of the pixels in the same block but not the pixels in its neighboring blocks  The “embeddability” of a block is invariant in the watermark embedding process The “flippability” of a pixel is invariant in the watermark embedding process A “flippable” pixel which is identified as “embeddable” is still “flippable,” hence an “embeddable” block remains “embeddable”  The watermark can be extracted blindly from the “embeddable” blocks by computing the odd-even feature of the number of black or white pixels

20.  Introduction  Proposed Method  The Authentication Mechanism Locate “Embeddable” Pixels Criterion Authentication Process The Verification Process  Experimental Results  Conclusions

21. Locate “Embeddable” Pixels Criterion  The odd-even enforcement is employed for the watermark embedding Vulnerable to the “parity attack” Ex: an adversary can carefully flip two pixels in the same block while keeping the odd-even feature of the block unchanged.

22. Locate “Embeddable” Pixels Criterion  p-4 condition Flipping the pixel that does not change the “flippability” of its previous four (p-4) neighbors that lie in the same 3 x 3 block  d-2 condition Flipping the pixel that does not affect the “embeddability” of those d-2 pixels (determined pixel) that have already been processed in the same block

23. Locate “Embeddable” Pixels Criterion

24. Authentication Process

25. The Verification Process

26.  Introduction  Proposed Method  The Authentication Mechanism  Experimental Results Capacity and Visibility Test Locating Embeddable Pixels Criterion and Authentication Mechanism Comparisons  Conclusions

27. Capacity and Visibility

29. (a)The original text image of size 336 x 336 (Chinese) (d) Hide 482 bits by FB 3 x 3 (e) Hide 733 bits by NIB 4 x 4 (f) Hide 1261 bits by IB 4 x 4

30. Capacity and Visibility (b) The original text image of size 336 x 336 (English) (g) Hide 447 bits by FB 3 x 3 (h) Hide 672 bits by NIB 4 x 4 (i) Hide 1237 bits by IB 4 x 4

31. Capacity and Visibility (b) The original text image of size 336 x 336 (Handwritten) (g) Hide 313 bits by FB 3 x 3 (h) Hide 554 bits by NIB 4 x 4 (i) Hide 972 bits by IB 4 x 4

32. Capacity and Visibility  Evaluate the visual distortion caused by flipping pixels The visual distortion table proposed by Wu et al. is employed. M. Wu and B. Liu, “Data hiding In binary images for authentication and annotation,” IEEE Trans. Multimedia, vol. 6, no. 4, pp. 528–538, Aug. 2004.

33. Capacity and Visibility  Distortion score (DS)  Total distortion (TD)  Average per pixel distortion (APPD)

34. Capacity and Visibility

35. Test Locating Embeddable Pixels Criterion and Authentication Mechanism (a)The original image of size 920 x 230 (b) Hide 1056 bits by proposed algorithm with FB 3 x 3 (c) The watermarked image that is tampered (d) The original logo image (e) The reconstructed logo image when no tampering occurs (f) The reconstructed logo image when the watermarked image has been tampered

36. Comparisons (a)Original image of size 173 x 115 (b) The proposed method (c) Wu et al. method (d) Tseng et al. (e) Lu et al. (f) Yang & Kot 111 bits 180 bits 260 bits

37.  Introduction  Proposed Method  The Authentication Mechanism  Experimental Results  Conclusions

38. Conclusions  A novel blind data hiding scheme for binary images authentication based on connectivity- preserving A window of 3 x 3 is employed to access the “flippablility” of a pixel in a block  Different types and sizes of block can be chosen cater for different applications  The proposed scheme can be applied to a wide variety of binary image authentication