1. 1. Priyanka Sharma
2. 2. Introduction The process of embedding information into a digital signal in a way that is difficult to remove. The signal may be text, images, audio, video. The information is also carried in the copy if the signal is copied.
3. 3. Example:
4. 4. GENERAL APPLICATIONS Copyright Protection To prove the ownership of digital media.
5. 5. Tamper proofing To find out if data was tampered. GENERAL APPLICATIONS
6. 6. Quality Assessment Degradation of Visual Quality Loss of Visual Quality GENERAL APPLICATIONS
7. 7. LIFE-CYCLE PHASES Attemp to extract watermark from signal The marked signal is modified Produce watermarke d signal
8. 8. CLASSIFICATION Digital watermarking techniques can be classified in many ways : Visibility Robustness Perceptibility Capacity Embedding method
9. 9. VISIBILITY Visible Text or a logo which identifies the owner of the media. Invisible Information is added as digital data to audio, picture or video, but it cannot be perceived. May be a form of Steganography.
10. 10. ROBUSTNESS Robust Resisted a designated a class of transformations. Against adversary based attack. (e.g. noise addition to images) Used in copy protection application. Example: Robust Private Spatial Watermarks
11. 11. SPECIFIC WATERMARKING TECHNIQUES ON IMAGES
12. 12. A very simple yet widely used technique for watermarking images is to add a pattern on top of an existing image. Usually this pattern is an image itself - a logo or something similar. SIMPLE WATERMARKING
13. 13. Bit Plane Slicing Examine the contribution of each bit For PGM images each pixel is an eight bit value A bit plane is a binary image representing each bit
14. 14. Watermarking in the frequency domain involves selecting the pixels to be modified based on the frequency of occurrence of that particular pixel. Transform an image into the frequency domain. A block-based DCT watermarking approach is implemented. An image is first divided into blocks and DCT is performed on each block. The watermark is then embedded by selectively modifying the middle- frequency DCT coefficients. FREQUENCY-BASED TECHNIQUES
15. 15. What is DCT ? Formally, the discrete cosine transform (DCT) is a linear, invertible function F : RN -> RN (where R denotes the set of real numbers), or equivalently an invertible N N square matrix FREQUENCY-BASED TECHNIQUES
16. 16. FREQUENCY-BASED TECHNIQUES
17. 17. Discrete wavelet transform (DWT) The image is separated into different resolution The original image is high-pass filtered, yielding the three large images, each describing local changes details in the original image It is then low-pass filtered and downscaled, yielding an approximation image. This image is high-pass filtered to produce the three smaller detail images. And low-pass filtered to produce the final approximation image in the upper-left. WAVELET WATERMARKING TECHNIQUES
18. 18. WAVELET WATERMARKING TECHNIQUES
19. 19. Embedding the watermark The host image and watermark are transformed into wavelet domain. The transformed watermark coefficients were embedded into those of host image at each resolution level with a secret key. WAVELET WATERMARKING TECHNIQUES
20. 20. WAVELET WATERMARKING TECHNIQUES
21. 21. Attacking Methods
22. 22. Attacks on Watermark Transmission Lossy Other Compression International TamperingsProcessing I I' Watermarked Object Corrupted Object Transmission Typical Distortions and International Tampering Geometrical Distortion Common Signal Figure provided by Cox et al. [1].
23. 23. Attacks on Watermark Transmission Lossy Other Compression International TamperingsProcessing I I' Watermarked Object Corrupted Object Transmission Typical Distortions and International Tampering Geometrical Distortion Common Signal Irreversible Data Loss Quality Degradation e.g. JPEG/MPEG
24. 24. Attacks on Watermark Transmission Lossy Other Compression International TamperingsProcessing I I' Watermarked Object Corrupted Object Transmission Typical Distortions and International Tampering Geometrical Distortion Common Signal Specific for images/videos rotation, translation, scaling, and cropping operations
25. 25. Attacks on Watermark Transmission Lossy Other Compression International TamperingsProcessing I I' Watermarked Object Corrupted Object Transmission Typical Distortions and International Tampering Geometrical Distortion Common Signal analog-to-digital, digital-to-analog conversion, etc.
26. 26. Attacks on Watermark Transmission Lossy Other Compression International TamperingsProcessing I I' Watermarked Object Corrupted Object Transmission Typical Distortions and International Tampering Geometrical Distortion Common Signal Rewatermarking
27. 27. Desired Characteristics of Invisible Watermarks 1. Perceptually unnoticeable 2. Robust to common watermark attacks 3. Quality degradation upon removal of watermarks 4. Unambiguously identifies the owner of the digitized medium (audio, video, or image).
28. 28. Example (1) Original (2) Watermarked Differences of (1) & (2)
29. 29. Advantages & Disadvantages Advantages: Not noticeable since the watermarks are spread out. Cant be removed without severe quality degradation since watermarks are inserted at perceptually significant regions. Disadvantages: Original watermark is required in the extraction process.
30. 30. References: [1]Ingemar J. Cox, et al., Secure Spread Spectrum Watermarking for Multimedia, IEEE Trans. on Image Processing, Vol. 6, No.12, Dec 1997, pp.1673-1687. [2] Saraju P. Mohanty, Digital Watermarking: A Tutorial Review, Department of Computer Science and Engineering, University of South Florida. [3] Peter Meerwald, Digital Image Watermarking in the Wavelet Transform Domain, Masters Thesis, Department of Scientific Computing, University of Salzburg, Austria, January 2001. [4] http://www.cosy.sbg.ac.at/~pmeerw/Watermarking/source/
31. 31. The End