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Improving Watermarking Robustness Against Print and Scan Attack

Amiri, Hamid | 2009

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 39001 (19)
  4. University: Sharif University of Technology
  5. Department: Computer Engineering
  6. Advisor(s): Jamzad, Mansour
  7. Abstract:
  8. The advent of digital age with the Internet revolution has made it extremely convenient for users to access, create, process, copy, or exchange multimedia data. This has created an urgent need for protecting intellectual property in both the digital and the print media. Digital watermarking is a suitable way to do this. In this technology, some hidden information called watermark are embedded into host signal and extracted to confirm copyright protection. However, the watermark should be embedded in the host in such a way that the attacks could not destroy it. Print and scan is a popular attack that is applied on digital images. This attack has complex nature and can be implemented easily. In this thesis, firstly, we study the print and scan operations by a modeling algorithm. The aim of the model is to simulate the processes of noise addition and non-liner transforms imposed on the printed and scanned image. Using this model, we can suggest a watermarking algorithm that will be robust with respect to this attack. We propose two robust watermarking algorithms in wavelet domain where watermark is embedded in the lowest detail subbands of original image after three level decomposition on it. In first method, coefficients with high magnitude are extracted and watermark bits are embedded into these coefficients. To extract the watermark in this method, we need the positions of coefficients that are used in embedding phase. If there aren't geometric distortions when printed image is scanned, this method has high robustness. In second method, discrete cosine transform (DCT) is applied on wavelet subbands to extract suitable coefficients for watermarking. This is a blind method and in extracting phase it needs less information in contrast to the first method. This method has high robustness against print and scan attack and preserves its robustness even in presence of geometric attacks such as rotation and ransformation
  9. Keywords:
  10. Image Watermarking ; Quality ; Modeling ; Wavelet Transform ; Robust Watermarking ; Robustness ; Print and Scan

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