EE 5359 Multimedia Processing Project Proposal DIGITAL WATERMARKING Under guidance of Dr K R Rao Submitted By Abrar Ahmed Syed 1000614216 abrar syed mavs uta edu The University of Texas at Arlington DIGITAL WATERMARKING Abstract Everyday tons of data is embedded on digital media or distributed over the internet The data so distributed can easily be replicated without error putting the rights of their owners at risk Even when encrypted for distribution data can easily be decrypted and copied One way to discourage illegal duplication is to insert information known as watermark into potentially vulnerable data in such a way that it is impossible to separate the watermark from the data 1 0 Introduction of Digital Watermarking Embedding a digital signal audio video or image with information which cannot be removed easily is called digital watermarking As many advances were made in the field of communication it became rather simple to decrypt a cipher text Hence more sophisticated methods were designed to offer better security than what cryptography could offer This led to the discovery of stenography and watermarking Stenography is the process of hiding information over a cover object such that the hidden information cannot be perceived by the user Watermarking is closely related to steganography but in watermarking the hidden information is usually related to the cover object Hence it is mainly used for copyright protection and owner authentication Figure 1 explains how watermarking is derived from steganography Figure 1 Types of Steganography 1 1 1 Basic Principle A watermarking system is usually divided into three distinct steps embedding attack and detection In embedding an algorithm accepts the host and the data to be embedded and produces a watermarked signal The watermarked signal is then transmitted or stored usually transmitted to another person If this person makes a modification this is called an attack There are many possible attacks Detection is an algorithm which is applied to the attacked signal to attempt to extract the watermark from it If the signal was not modified during transmission then the watermark is still present and it can be extracted If the signal is copied then the information is also carried in the copy The embedding takes place by manipulating the content of the digital data which means the information is not embedded in the frame around the data it is carried with the signal itself Figure 2 shows the basic block diagram of Watermarking process Figure 2 Watermarking Block Diagram The original image and the desired watermark are embedded using one of the various schemes that are currently available The obtained watermarked image is passed through a decoder in which usually a reverse process to that employed during the embedding stage is applied to retrieve the watermark The different techniques differ in the way in which it embeds the watermark on to the cover object A secret key is used during the embedding and the extraction process in order to prevent illegal access to the watermark 2 0 Applications Ownership Assertion to establish ownership of the content i e image 1 Fingerprinting to avoid unauthorized duplication and distribution publicly 1 Authentication and integrity verification the authenticator is inseparably bound to the content whereby the author has a unique key associated with the content and can verify integrity of that content by extracting the watermark 1 Content labeling bits embedded into the data that gives further information 1 Usage control added to limit the number of copies created 1 Content protection content stamped with a visible watermark that is very difficult to remove so that it can be publicly and freely distributed 1 3 0 Classifications 3 1 Visible Any text or logo to verify or hide content Fw 1 F W 12 Fw Watermarked Image constant 0 1 IF 0 No watermark if 1 Wateramark F original image W watermark 3 2 Invisible This is hidden in the signal or content It cannot be perceived by human eye or ear Usually used for authentication or security Robust Invisible watermark cannot be manipulated without disturbing the host signal This is by far the most important requirement of a watermark There are various attacks unintentional cropping compression scaling and unintentional attacks which are aimed at destroying the watermark So the embedded watermark should be such that it is invariant to various such attacks Fragile Watermark fails with even the slightest modification to it Public Resists benign transformation but fails when it is attacked by a malignant modification 3 3 Capacity It is based on length of the embedded signal Zero Bit It denotes 1 or 0 based whether watermark is present or absent Also called Italic zero bit watermarked signal N Bit It is N Bit long m m1 mn with n m or M 0 1 n It is a modulated watermark Also known as non zero length watermark 3 4 Perceptibility A watermark is called imperceptible if the original cover signal and the marked signal are perceptually indistinguishable A watermark is called perceptible if its presence in the marked signal is noticeable 3 5 Embedding Techniques Spread Spectrum If obtained by additive modification It is robust It has low information capacity due to host interference Quantization Marking is done by quantizing It is less robust but can carry a large data since it has very little interference from the host signal Amplitude Modification If marked signal is embedded by additive modification spread spectrum but is particularly done in spatial domain Similar to 4 0 Techniques or Schemes of Watermarking 4 1 Spatial Domain Spatial domain watermarking slightly modifies the pixels of one or two randomly selected subsets of an image Modifications might include flipping the low order bit of each pixel However this technique is not reliable when subjected to normal media operations such as filtering or lossy compression 9 LSB Coding Least significant bit substitute with watermark As the names suggest the host signals least significant bit is modified Predictive Coding Proposed by Matsui and Tanaka 3 In this method Correlation between adjacent images is exploited A set of pixels where the watermark has to be embedded is chosen and alternate pixels are replaced by the difference between the adjacent pixels This can be further improved by adding a constant to all the differences A cipher key is created which enables the retrieval of the embedded watermark at the receiver Co relation
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