1. 1 LSB Matching Revisited Source: IEEE Signal Processing Letters (Accepted for future publication) Authors: Jarno Mielikainen Speaker: Chia-Chun Wu ( 吳佳駿 ) Date: 2006/03/13

2. 2 Outline Introduction LSB replacement The proposed scheme Experimental results Conclusions Comments

3. 3 Introduction Steganographic Internet Secret message: 01011001110… Cover image Stego image

4. 4 LSB replacement 162150 1010001010010110 xixi x i+1 10 mimi m i+1 1010001110010110 163150 yiyi y i+1

5. 5 The proposed scheme Modified version of the LSB method Binary function f (l, n) Property 1: Property 2:Example: f (162, 150) = 1 f (161, 150) = 0 f (163, 150) = 1 f (162, 150) = 1 f (162, 151) = 0

6. 6 Embedding algorithm Embedding algorithm for a pair of pixels.

7. 7 Embedding messages (1/3) 162150 1010001010010110 xixi x i+1 1001011110100010 151162 yiyi y i+1 00 mimi m i+1 Case 1: embedding “0”, “0” 10 mimi m i+1 1001011010100010 150162 Case 2: embedding “0”, “1” yiyi y i+1

8. 8 Embedding messages (2/3) 162150 1010001010010110 xixi x i+1 10 mimi m i+1 1010000110010110 161150 f (161, 150) = 0 f (163, 150) = 1 Case 3: embedding “1”, “0” yiyi y i+1

9. 9 Embedding messages (3/3) 162150 1010001010010110 xixi x i+1 11 mimi m i+1 1010001110010110 163150 Case 4: embedding “1”, “1” f (161, 150) = 0 f (163, 150) = 1 yiyi y i+1

10. 10 Extracting messages yiyi y i+1 LSB ( y i ) f ( y i, y i+1 ) 16215100 16215001 16115010 16315011 162150 xixi x i+1

11. 11 Example - 1 xixi x i+1 mimi m i+1 yiyi y i+1 110021 110101 111010 or 2 111111 120002 120122 121012 121111 or 3

12. 12 Example - 2 xixi x i+1 mimi m i+1 yiyi y i+1 210021 210120 or 2 211031 211111 220021 or 3 220122 221012 221132

13. 13 Experimental results (1/2) 1000 JPEG images All size 384×256 HCF COM detectors The center of mass (COM) of the histogram characteristic function (HCF) introduced by Harmsen et al. [4] Ker [5] proposed using the adjacency histogram instead of the usual histogram.

14. 14 Experimental results (2/2) ROC curves for the calibrated HCF COM. The x-axis has been scaled to focus on a region of interest. ROC curves for the calibrated adjacency HCF COM.

15. 15 Conclusions The proposed method allows an embedding of the same amount of information into the stego image as LSB matching but with fewer changes to the cover image. The detection of the existence of the hidden messages using the HCF COM-based detectors is less efficient against the method compared to LSB matching.

16. 16 Comments The embedding cannot be performed for saturated pixels, i.e., pixels that have either a minimal (0) or maximal (255) allowable value.