Digital watermarking technique for protecting digital images Nibedita Sahoo M.Tech (ICT) Roll no.-10IT61B01

Agenda Watermark and digital watermarking Basic characteristic Watermark attacks Watermarking technique Spatial Domain watermarking Transform Domain Watermarking Techniques Current application area Future trends Conclusion Reference

What is watermark? A distinguishing mark impressed on paper during manufacture; visible when paper is held up to the light (e.g. $ Bill)

What is digital watermarking? In generally digital watermarking is a technique for inserting information into an image. It is an evolving field that requires continuous effort to find the best possible method in protecting multimedia content. It is a process of embedding information into digital multimedia content such that the information can later be extracted or detected for variety of purposes including identification and authentication.

Block diagram for watermarking digital image Original image Embedding procedure Watermark digital image

Example : Digital watermarking Original image Watermark Digital watermarking

Basic characteristic of digital watermarking Capacity The optimum amount of data that can be embedded in a given signal. Robustness We embed and retrieve data such that it would survive malicious or accidental attempts. Security We determine that the information embedded has not been tampered, forged or even removed . Transparency The watermark is not visible in the image under typical viewing conditions.

Watermark Attacks Active Attacks Passive Attacks Forgery Attacks Hacker attempts to remove or destroy the watermark. Passive Attacks Hacker tries to find if a watermark is present. Removal of watermark is not an aim. Forgery Attacks Hacker tries to embed a valid watermark. Serious in authentication. If hacker embeds a valid authentication watermark, watermark detector can accept modified media.

Types of watermarking techniques

1.According to working domain Spatial domain Direct usage of data to embed and extract Watermark. Spatial watermarking can also be applied using color separation. In this way, the watermark appears in only one of the color bands. This renders the watermark visibly subtle such that it is difficult to detect under regular viewing. However, the mark appears immediately when the colors are separated for printing. Frequency Domain This technique is motivated by both perceptual transparency and watermark robustness. This technique is very effective both in terms transparency, robustness to signal processing.

2.According to the type of document Image Watermarking Video Watermarking Audio Watermarking Text Watermarking

3.According to the human perception Visible watermark In visible digital watermarking, the information is visible in the picture or video. Typically, the information is text or a logo, which identifies the owner of the media. Invisible-Robust watermark Information is added as digital data to audio, picture, or video, but it cannot be perceived. Invisible-Fragile watermark A fragile marking system should be able to detect any changes made in a marked image after marking. Fragile watermarking is mainly used for integrity protection, which must be very sensitive to the changes of signal.

4.According to application source based Source-based watermark are desirable for ownership identification or authentication where a unique watermark identifying the owner is introduced to all the copies of a particular image being distributed. Destination based In case of destination based where each distributed copy gets a unique watermark identifying the particular buyer. The destination based watermark could be used to trace the buyer in the case of illegal reselling. (EX- FINACLE SOFTWARE BY INFOSYS)

Digital Image Processing An image is a 2-D Signal – Spatial signal – Intensity value as I(X,Y) Digital image – Digitized 2-D signal Use rectangular shape areas called pixels Digital representation: 8-bit, 12-bit, 16-bit, …

Review of Digital Image Processing Digital images are represented using matrices:

Types Watermarking The hidden message may be added in Spatial Domain Discrete Fourier Transform (DFT) Domain Discrete Cosine Transform (DCT) Domain Discrete Wavelet Transform Domain (DWT)

Spatial domain Watermarking The term spatial domain refers to the aggregate of pixel composing an image. Spatial domain methods are procedures that operate directly on the pixels. Watermark message M(x,y) – Random or pseudo random signal – Binary { -1,+1} or { -1, 0, +1} – other signals are used Watermark message is added linearly as: W(x,y)= I(x,y)+kM(x,y)

Contd. The watermark message is added in the spatial Domain: IM (x, y) = I (x, y) + kM(x, y)

Spatial Domain Watermark Embedding Scheme Overview: We will first embed the watermark into X and then redirect the watermark to the saturation component of the image . Our original image, f is a color image of size MxN and will be represented by :f = { f(x,y), 0 ≤ x < M, 0 ≤ y < N} Our watermark will be a image of size M/8xN/8. It is represented by:W={W(i,j),0≤ i<M/8, 0≤ j<N/8}.

Contd. Step 1: Find the achromatic component of the host image Compute the achromatic component of a color image . Step 2: Break the achromatic image into blocks. Step 3:Perform a permutation of the watermark to reduce its vulnerability. Step 4:Embed the watermark into the Achromatic Component. Step 5: Redirect the Watermark into the Saturation Component of the Color Image.

Spatial Domain Watermark Extraction Scheme This type of extraction is called a nonblind extraction because original image, along with the watermarked image, are needed to extract the watermark. Step 1: Find Achromatic Component of Original Image Step 2: Reverse the Saturation Adjustment and Find the Achromatic Component of the Watermarked Image. Step 3: Break the achromatic components into blocks. Step 4: Extract the permuted Watermark. Step 5: Reverse Pseudorandom Permutation.

THE PROPOSED MODEL

Transform Domain Watermarking Transform domain watermarking techniques are more robust in comparison to spatial domain methods. Among the transform domain watermarking techniques discrete wavelet transform (DWT) based watermarking techniques are gaining more popularity because DWT has a number of advantages over other transform such as progressive and low bit-rate transmission, quality scalability . The watermark message is inserted in the transform domain. Different transforms behaves differently to different attacks.

Transform Domain Watermarking Discrete Fourier Transform (DFT) is superior for shifting attacks- Shifting in the space domain leads to a phase shift in the frequency domain.

Transform Domain Watermarking Discrete Cosine Transform (DCT) Supports block-based transform (8x8),(16x16), (32x32), … Compacts the energy of each block according to its frequency content. Used in JPEG compression The watermark message is embedded in the intermediate frequency coefficients. Example of adding watermark image to the intermediate frequency of each block.

Transform Domain Watermarking Discrete Cosine Transform – Example of adding watermark image to the intermediate frequency of each block

Transform Domain Watermarking Discrete Wavelet Transform (DWT) DWT locally separates the content of the image into low frequency and high frequency subbands. Most of the energy is concentrated in the low frequency subband. In watermarking: The message is inserted in the high frequency subbands (HL,LH and HH)

Transform Domain Watermarking Non-Regular Transform – Spreads the energy content into different subbands – The subbands are similar to the original image Similar images Similar histogram

Application Ownership assertion Watermarks can be used for ownership assertion. Copy prevention or control Recording device may inhibit recording a signal if detected watermark indicates that it is prohibited. DVD video and digital music distribution. Secret Communications Hide information such that general public do not know its presence.

Application Authentication Broadcast Monitoring Fingerprinting Detect If image/video has been altered Broadcast Monitoring Keep track of when and where an advertisement is played. Fingerprinting Identify the source of an illegal copy. Unique watermark embedded in each copy

Future trends A number of companies, such as Sony and IBM have introduced digital watermarking software applications that allow individuals to imbed watermarks within image, audio and video files to protect them from copyright. Companies are also offering on-line tracking services so that the copyright owner can see how the owner's materials are used via the Web.

Conclusion As described recent developments in the digital watermarking of images in which the watermarking technique is invisible. Digital watermarking is a rapidly evolving area of research and development. Digital watermarking technology can provide a new way to protect the copyright of multimedia information and to ensure the safe use of multimedia information.

Reference http://en.wikipedia.org/wiki/Steganography http://en.wikipedia.org/wiki/Digital_watermark W. Bender D. Gruhl N. Morimoto and A. Lu. Techniques for data hiding. IBM Systems Journal, 35(3-4):313–336, 1996. [2] S. Bhattacharjee, “Compression Tolerant Image Authentication”, Proceedings, Int. Conf. Image Proc., Chicago, Oct. 1998.

Reference S.P. Mohanty, et aI., "A Dual Watennarking Technique for Images", Proc. 7th ACM International Multimedia Conference, ACM-MM'99, Part 2, pp. 49-51, Orlando, USA, Oct. 1999. [2] I. Cox, J. Kilian, F. T. Leighton, and T. Shamoon, "Secure spread spectrum watennarking for multimedia," IEEE Transactions on Image Processing, vol. 6, no. 12, December, 1997, pp. 1673-1687. [3] F. M. Boland, J. J. K. 6 Ruanaidh and C. Dautzenberg, "Watennarking digital images for copyright protection," Proceedings of the International Conference on Image Processing and its Applications, Edinburgh, Scotland, July 1995, pp. 321-326.

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