EE 5359 Multimedia Processing Project ProposalDIGITAL WATERMARKINGUnder guidance of Dr.K.R.RaoSubmitted By,Abrar Ahmed [email protected] University of Texas at ArlingtonDIGITAL WATERMARKINGAbstractEveryday tons of data is embedded on digital media or distributed over the internet. Thedata so distributed can easily be replicated without error, putting the rights of their owners atrisk. Even when encrypted for distribution, data can easily be decrypted and copied. One way todiscourage illegal duplication is to insert information known as watermark, into potentiallyvulnerable data in such a way that it is impossible to separate the watermark from the data.1.0 Introduction of Digital WatermarkingEmbedding a digital signal (audio, video or image) with information which cannot beremoved easily is called digital watermarkingAs many advances were made in the field of communication it became rather simple todecrypt a cipher text. Hence more sophisticated methods were designed to offer better securitythan 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 hiddeninformation 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 ismainly used for copyright protection and owner authentication. Figure 1 explains howwatermarking is derived from steganography.Figure 1. Types of Steganography [1]1.1 Basic PrincipleA 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. Thereare 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, thenthe 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, itis 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 schemesthat are currently available. The obtained watermarked image is passed through a decoder inwhich usually a reverse process to that employed during the embedding stage is applied toretrieve the watermark. The different techniques differ in the way in which it embeds thewatermark on to the cover object. A secret key is used during the embedding and the extractionprocess 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 canverify 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 Classifications3.1 Visible Any text or logo to verify or hide contentFw= (1-α) F+ α*W [12]Fw = Watermarked Imageα =constant ; 0<=α<=1 , IF α=0 No watermark, if α=1 WateramarkF =original imageW =watermark3.2 InvisibleThis is hidden in the signal or content. It cannot be perceived by human eye or ear. Usuallyused 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 aimedat destroying the watermark. So, the embedded watermark should be such that it isinvariant 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 malignantmodification.3.3 CapacityIt is based on length of the embedded signal.- Zero-Bit: It denotes 1 or 0 based whether watermark is present or absent. Also calledItalic 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 PerceptibilityA 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 informationcapacity due to host interference.-Quantization: Marking is done by quantizing. It is less robust but can carry a large data since ithas very little interference from the host signal.-Amplitude Modification: If marked signal is embedded by additive modification. Similar tospread spectrum but is particularly done in spatial domain.4.0 Techniques or Schemes of Watermarking4.1 Spatial DomainSpatial domain watermarking slightly modifies the pixels of one or two randomly selectedsubsets 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 asfiltering or lossy compression [9]- LSB Coding: Least significant bit substitute with watermark. As the names suggest, thehost signals least significant bit is modified.- Predictive Coding: Proposed by Matsui and Tanaka. [3] In this method Correlationbetween adjacent
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