1. Watermarking Text Document Images Using Edge Direction Histograms Young-Won Kim and Il-Seok Oh Pattern Recognition Letters, Vol. 25, 2004, pp. 1243 – 1251 Reporter: Jen-Bang Feng

2. 2 Outline Data Hiding vs. Watermark vs. Authentication Related Works The Proposed Scheme Experimental Results Comments

3. 3 Watermark Purpose: Copyright protection for digital media Considerations: Embed watermark into media Retrieve watermark against attacks (capacity is not important relatively) WM + Original image Protected image Embed tested image Retrieve WM ’

4. 4 Data Hiding vs. Watermark vs. Authentication Data Hiding (Steganographic) Hide data in media Request high capacity Watermark Copyright protection for media Request high robust Authentication Check the correctness of media Request high sensitive

5. 5 Related Works Character-level methods Brassil et al. (1999) moves a line (word) upward or downward (left or right) depending on the binary signal Huang and Yan (2001) modifes the inter-word spaces Feature-level methods Amano and Misaki (1999) modifying features such as stroke ( 筆觸 ) width or serif ( 截線 ) shape Brassil et al. (1994) adjusts the height of the vertical strokes of characters such as b, d, and h Pixel-level methods Bhattacharjya and Ancin, (1999) an image is partitioned into a set of 3x3 sites and one bit is inserted per two sites upward downward

6. 6 The Proposed Scheme For grayscale text document images Modify the distribution of edges

7. 7 The Proposed Scheme 1. Edge detection

8. 8 The Proposed Scheme 2. Change the distribution of edges 0 is embedded1 is embedded

9. 9 The Decoding Process Δ > 0: 0 is embedded Δ < 0: 1 is embedded H m : ratio of mother histogram H c : ratio of child histogram

10. 10 Experimental Results

11. 11 Experimental Results

12. 12 Experimental Results

13. 13 Comments Should not need the original image Can be modified and used for authentication Filled ratio?