Watermarking converted 1.docx

1. INTRODUCTION

Watermarking is the process that embeds data called a watermark, tag or label into a multimedia object such that watermark can be detected or extracted to make an assertion about the object may an image or video or audio may also be text only. A watermark can be perceived as an attribute of the carrier (cover). It may contain information such as copyright, license, tracking and authorship etc. Whereas in case of stenography, the embedded message may have nothing to do with the cover. Digital watermarking differs from digital fingerprinting.Nowadays cases involving fake currency are increasing rapidly, so no one needs to be reminded of the importance of watermarking. A watermark is a form, image or text that is impressed onto paper, which provides evidence of its authenticity. Digital watermarking is an extension of this concept in the digital world. In recent years, the rapid growth of the Internet has highlighted the need for mechanisms to protect ownership of digital media. Exactly identical copies of digital information, be it images, text or audio, can be produced and distributed easily. In such a scenario, how can we identify that who is the actual owner? It was impossible to tell until now, but now its possible only because of Digital Watermarking.2. HISTORY OF WATERMARKING

More than 700 years ago, paper watermarks were used in Fabriano, Italy to indicate the paper brand and the mill that produced it. After that they were used to indicate the paper format, quality and strength. By the 18th century it was used as measures on money and other documents to avoid from duplicating it. They are still widely used as security features in currency today.The term watermark was introduced near the end of the 18th century. It was probably given this name because the marks resemble the effects of water on paper.

What is WatermarkA watermark is a pattern of bits inserted into a digital image, audio, video or text file that identifies the file's copyright information like author, rights etc. The name comes from the visible watermarks imprinted on the product that identify the manufacturer of the product. The purpose of digital watermarks is to provide copyright protection for once property that's in digital format.

3. FRAMEWORK FOR WATERMARKING

Watermarking is the process that embeds data called a watermark or digital signature or tag or label into a multimedia object such that watermark can be detected or extracted later to make an assertion about the object. The object may be an image or audio or video. A simple example of a digital watermark would be a visible seal placed over an image to identify the copyright. However the watermark might contain additional information including the identity of the purchaser of a particular copy of the material. In general, any watermarking scheme ;(algorithm) consists of three parts.The watermark.The encoder (insertion algorithm).The decoder and comparator (verification or extraction or detection algorithm).Each owner has a unique watermark or an owner can also put different watermarks in different objects the marking algorithm incorporates the watermark into the object. The verification algorithm authenticates the object determining both the owner and the integrity of the object.

3.1 ENCODING PROCESS

Let us denote an image by a signature by S= s1,s2and the watermarked image by I. E is an encoder function, it takes an image I and a signature S, and it generates a new image which is called watermarked image , mathematically,

It should be noted that the signature S may be dependent on image I. In such cases, the encoding process described by Eqn. 1 still holds. Following figure illustrates the encoding process.

3.2 DECODING PROCESSA decoder function D takes an image J (J can be a watermarked or un-watermarked image, and possibly corrupted) whose ownership is to be determined and recovers a signature from the image. In this process an additional image I can also be included which is often the original and un-watermarked version of J. This is due to the fact that some encoding schemes may make use of the original images in the watermarking process to provide extra robustness against intentional and unintentional corruption of pixels. Mathematically the extracted signature will then be compared with the owner signature sequence by a comparator function and a binary output decision generated. It is 1 if there is match and 0 otherwise, which can be represented as follows. Where is the core relator is the correlation of two signatures and 0 is certain threshold. Without loss of generality, watermarking scheme can be treated as a three-tupple

A watermark must be detectable or extractable to be useful. Depending on the way the watermark is inserted and depending on the nature of the watermarking algorithm, the method used can involve very distinct approaches. In some watermarking schemes, a watermark can be extracted in its exact form, a procedure we call watermark extraction. In other cases, we can detect only whether a specific given watermarking signal is present in an image, a procedure we call watermark detection. It should be noted that watermark extraction can prove ownership whereas watermark detection can only verify ownership.

4. FEATURES OF WATERMARKING

Watermarking techniques are useful for embedding metadata in multimedia content. However, for inserting visible marks in images & video and for adding information about audio in audio clip etc. the digital watermarking technique is used, since it provides following main features.

Imperceptibility:

In watermarking, we traditionally seek high fidelity, i.e. the watermarked work must look or sounds like the original.

Robustness:

It is the property that the watermark should be able to survive any reasonable processing inflicted on the carrier (carrier here refers to the content being watermarked).

Security:

The watermarked image should not reveal any clues of the presence of the watermark, with respect to un-authorized detection.

Capacity:

The amount of embedded information must be large enough to uniquely identify the owner of the document or to uniquely distinguish all copies of the document.Multiple Watermarks:

If the watermarking algorithm allows for multiple watermarks then they must be detected independently of each other.

5. EFFECTIVE WATERMARKS

Features of a Good WatermarkThe following are features of a good watermark:1. It should be difficult or impossible to remove a watermark withoutnoticeably degrading thewatermarked content.2. This is to ensure that the copyright information cannot be removed3. The watermark shouldbe robust. This means that it should remain in the content after various types of manipulations ,bothintentional (knownasattacksonthewatermark) and unintentional (alterations that the digital data item would undergo regardless of whether it contains a watermark or not). These are describedbelow.Ifthewatermarkisafragilewatermark, however, it should not remain in the digital data after attacks on it ,but should be able to survive certain other alterations (as in the case of images, where it should be able to survive the common image alteration of cropping).4. Thewatermarkshouldbeperceptuallyinvisible,ortransparent. That is, it should be imperceptible (if it is of the invisible type). Embedding the watermark signal in thedigital data

6. HOW WATERMARKING IS DIFFERENT FROM STEGANOGRAPHY AND CRYPTOGRAPHY.

6.1. Steganography vs. Watermarking

Watermarking is not a new technique. It is descendent of a technique known as Steganography. Steganography is a technique for concealed communication i.e. the existence of the message that is communicated is a secret and its presence is known only by parties involved in the communication.

In Steganography a secret message is hidden within another unrelated message and then communicated to the other party. While in Watermarking again one message is hidden in another, but two messages are related to each other in some way.

Steganographic methods are in general not robust, i.e., the hidden information cannot be recovered after data manipulation. Watermarking, as opposed to steganography, has the additional feature of robustness against attacks. Even if the existence of the hidden information is known it is difficultideally impossiblefor an attacker to destroy the embedded watermark.

6.2. Cryptography vs. Watermarking

Watermarking is a totally different technique from cryptography. Cryptography only provides security by encryption and decryption. However, encryption cannot help the seller monitor how a legitimate customer handles the content after decryption. So there is no protection after decryption. Unlike cryptography, watermarks can protect content even after they are decoded.

Other difference is cryptography is only about protecting the content of the messages. Because watermarks are inseparable from the cover in which they are embedded, so in addition to protecting content they provide many other applications also, like copyright protection, copy protection, ID card security etc.

Also the concept of breaking the system is different for cryptosystems and watermarking systems. A cryptographic system is broken when the attacker can read the secrete message. But Breaking of a watermarking system has two stages: 1.) the attacker can detect that watermarking has been used. 2.) The attacker is able to read, modify or remove the hidden message.

How watermarking is better than Digital Signatures.

In watermarking we embed metadata into the multimedia content directly in such a way that it needs not additional bandwidth. Historically, integrity and authenticity of digital data has been guaranteed through the use of digital signatures. In that we use header part of the document for signature embedding. So additional bandwidth is required, which increase overhead.

7. Classification of Watermarking Techniques:

Digital Watermarking techniques can be classified in a number of ways depending on different parameters. Various types of watermarking techniques are enlisted below. Each of the different types mentioned below have different applications.

Inserted Media Category: Watermarking techniques can be categorized on the basis of whether they are used for Text, Image, Audio or Video.

Robust & Fragile Watermarking: Robust watermarking is a technique in which modification to the watermarked content will not affect the watermark. As opposed to this, fragile watermarking is a technique in which watermark gets destroyed when watermarked content is modified or tampered with.

Visible & Transparent Watermarking: Visible watermarks are ones, which are embedded in visual content in such a way that they are visible when the content is viewed. Transparent watermarks are imperceptible and they cannot be detected by just viewing the digital content.

Public & Private Watermarking: In public watermarking, users of the content are authorized to detect the watermark while in private watermarking the users are not authorized to detect the watermark.

Asymmetric & Symmetric Watermarking: Asymmetric watermarking (also called asymmetric key watermarking) is a technique where different keys are used for embedding and detecting the watermark. In symmetric watermarking (or symmetric key watermarking) the same keys are used for embedding and detecting watermarks.

Steganographic & Non-Steganographic watermarking: Steganographic watermarking is the technique where content users are unaware of the presence of a watermark. In non steganographic watermarking, the users are aware of the presence of a watermark.Steganographic watermarking is used in fingerprinting applications while non steganographic watermarking techniques can be used to deter piracy.

Necessary Data for Extraction: On the basis of necessary data for extraction watermarks can be divided into two categories: Blind Informed In blind watermarking original document is not required during watermark detection process. But in informed original document is required.

Watermarking techniques

Most watermarking research and publications are focused on images. The reason might be that there is a large demand for image watermarking products due to the fact that there are so many images available at no cost on the World Wide Web, which needs to be protected.

To insert a watermark we can use spatial domain, frequency domain, wavelet domain or compression domain.

8. SPATIAL DOMAIN TECHNIQUES:

Techniques in spatial domain class generally share the following characteristics: The watermark is applied in the pixel domain. No transforms are applied to the host signal during watermark embedding. Combination with the host signal is based on simple operations, in the pixel domain. The watermark can be detected by correlating the expected pattern with the received signal.The main strengths of pixel domain methods are that they are conceptually simple and have very low computational complexities.

Some of the spatial domain techniques are:

9. LEAST SIGNIFICANT BIT (LSB) TECHNIQUE:

The most straightforward method of watermark embedding would be to embed the watermark into the least significant bits of the cover object. Given the extraordinarily high channel capacity of using the entire cover for transmission in this method, a smaller object may be embedded multiple times. Even if most of these are lost due to attacks, a single surviving watermark would be considered a success. The following fig shows an example of modifying LSB.

Image:11001010001101010001101000000000...

Watermark:1110...

Watermarked Image:

11001011001101010001101100000000...

Despite its simplicity, LSB technique brings a host of drawbacks. Although it may survive transformations such as cropping, any addition of noise or lossy compression is likely to defeat the watermark. An even better attack would be to simply set the LSB bits of each pixel to one, fully defeating the watermark with negligible impact on the cover object. Furthermore, once the algorithm is discovered, the embedded watermark could be easily modified by an intermediate party.

10. BINARY IMAGE WATERMARKING:

A binary image is a digital image that has only two possible intensity values for each pixel. The two values are often 0 for black, and either 1 or 255 for white.

In binary image watermarking we embed a binary watermark in binary image. Usually it is much difficult to embed a watermark in binary image than in gray scale or colored image. The reason is that for binary image we have only two bits per pixel. So, change in any bit will change the pixel entirely.

The two basic ways to embed data in binary image are by changing the values of individual pixels and by changing a group of pixels. The first approach flips a black pixel to white or vice versa. The second approach modifies such features as the thickness of strokes, curvature, relative positions, etc. This approach generally depends more on the types of images (e.g., text, sketches, etc.). Since the number of parameters that can be changed in this manner is limited, especially under the requirements of blind detection and invisibility, the amount of data that can be hidden is usually limited except for special types of images.

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11. FREQUENCY DOMAIN TECHNIQUES:

Here we can embed watermark in DCT (Discrete Cosine Transform), DFT (Discrete Frequency Transform) domains etc. The main strength offered by transform domain techniques is that they can take advantage of properties of alternate domains to address the limitations of pixel-based methods or to support additional features.

A possible disadvantage of spatial techniques is that they are not very robust against attacks. In addition to this, adaptive watermarking techniques are a bit more difficult in the spatial domain. Both the robustness and quality of the watermark could be improved if the properties of the cover image could similarly be exploited. For instance, it is generally preferable to hide watermarking information in noisy regions and edges of images, rather than in smoother regions. The benefit is two-fold; Degradation in smoother regions of an image is more noticeable to the HVS(Human Visual System), and becomes a prime target for lossy compression schemes.

Taking these aspects into consideration, working in a frequency domain of some sort becomes very attractive.

12. DCT WATERMARKING TECHNIQUES:

The classic and still most popular domain for image processing is that of the Discrete Cosine Transform, or DCT. The DCT allows an image to be broken up into different frequency bands, making it much easier to embed watermarking information into the middle frequency bands of an image. The middle frequency bands are chosen such that they avoid the most visual important parts of the image (low frequencies) without over-exposing themselves to removal through compression and noise attacks (high frequencies).

13. WAVELET WATERMARKING:

Most of the researchers focus on embedding watermark in wavelet domain because watermarks in this domain are very robust. The following is one of the wavelet based watermarking techniques

Xia, Boncelet and Arce proposed a watermarking scheme based on the Discrete Wavelet Transform (DWT). The watermark, modeled as Gaussian noise, was added to the middle and high frequency bands of the image. The decoding process involved taking the DWT of a potentially marked image. Sections of the watermark were extracted and correlated with sections of the original watermark. If the cross-correlation was above a threshold, then the watermark was detected. Otherwise, the image was decomposed into finer and finer bands until the entire, extracted watermark was correlated with the entire, original watermark. This technique proved to be more robust than the DCT method.

14. APPLICATIONS OF WATERMARKING:

14.1. Security:

In the field of data security, watermarks may be used for certification, authentication, and conditional access.

14.1.1 Certification:

It is an important issue for official documents, such as identity cards or passports. Digital watermarking allows to mutually link information on the documents. That means some information is written twice on the document, for instance, the name of a passport owner is normally printed in clear text and is also hidden as an invisible watermark in the photo of the owner. If anyone would intend to duplicate the passport by replacing the photo, it would be possible to detect the change by scanning the passport and verifying the name hidden in the photo does not match any more the name printed on the passport.

14.1.2 Authentication: The goal of this application is to detect alterations and modifications in an image. Suppose we have picture of a car that has been protected with a watermarking technology. And if, the same picture is shown but with a small modification, say, the numbers on the license plate has been changed. Then after running the watermark detection program on the tampered photo, the tampered areas will be indicated in different color and we can clearly say that the detected area corresponds to the modifications applied to the original photo.

14.1.3 Conditional access:For example conditional access to confidential data on CD-ROMs may be provided using digital watermarking technology. The concept consists of inserting a watermark into the CD label. In order to read and decrypt the data stored on the CD, the watermark has to be read since it contains information needed for decryption. If someone copies the CD, he will not be able to read the data in clear-text since he does not have the required watermark.

14.2 Copyright Protection:

Copyright protection inserts copyright information into the digital object without the loss of quality. Whenever the copyright of a digital object is in question, this information is extracted to identify the rightful owner. It is also possible to encode the identity of the original buyer along with the identity of the copyright holder, which allows tracing of any unauthorized copies.

14.3 Copy protection:Copy protection attempts to find ways, which limits the access to copyrighted material and/or inhibit the copy process itself. Examples of copy protection include encrypted digital TV broadcast, access controls to copyrighted software through the use of license servers and technical copy protection mechanisms on the media. A recent example is the copy protection mechanism on DVDs. However, copy protection is very difficult to achieve in open systems, as recent incidents (like the DVD hack) show.

14.4 Other applications:

Digital watermarks can also serve as invisible labels and content links. For example, photo development laboratories may insert a watermark into the picture to link the print to its negative. This way is very simple to find the negative for a given print. All one has to do is scan the print and extracted the information about the negative.

In order to distinguish between different copies, different watermarks are embedded into different copies of the same document. These marks are also called "digital fingerprints".

15. ATTACKS ON WATERMARKS

A watermarked image is likely to be subjected to certain manipulations, some intentional such as compression and transmission noise and some intentional such as cropping, filtering, etc.

Lossy Compression: Many compression schemes like JPEG and MPEG can potentially degrade the datas quality through irretrievable loss of data.Geometric Distortions: Geometric distortions are specific to images videos and include such operations as rotation, translation, scaling and cropping.Common Signal Processing Operations: They include the followings.

D/A conversionA/D conversionRe samplingRe quantizationDithering distortionRecompressionLinear filtering such as high pass and low pass filteringAddition of a constant offset to the pixel valuesAddition of Gaussian and Non Gaussian noiseLocal exchange of pixelsother intentional attacks:Printing and RescanningWatermarking of watermarked image (re watermarking)Collusion: A number of authorized recipients of the image should not be able to come together (collude) and like the differently watermarked copies to generate an un-watermarked copy of the image (by averaging all the watermarked images).

Forgery: A number of authorized recipients of the image should not be able to collude to form a copy of watermarked image with the valid embedded watermark of a person not in the group with an intention of framing a 3rd party.

16. DISADVANTAGES OF WATERMARKING:

Degrade image quality:

Even an invisible watermark will slightly alter the image during embedding. Therefore, they may not be appropriate for images, which contain raw data from an experiment. For example, embedding an invisible watermark in a medical scan might alter the image enough to lead to false diagnosis.

17. CONCLUSION

Digital watermarking has rapidly advanced from theory to practice. This report focuses on how watermarking techniques are advantageous over stegnography, cryptography and digital signatures, and also focuses on different types and domains of digital watermarking techniques.

A common application requirement for the watermarks is that they resist attacks that would remove it. Some of the watermarks being attack-resistant may be accidentally removed by unintended attacks such as cropping, reduction, or compression. There are also other techniques like blind watermarking (which uses multiple watermarks and also no need of original image at the of watermark recovery), which uses watermark nesting and encryption. Nesting means it embeds an extra watermark into the main watermark and then embeds the main watermark into the cover image.

Digital watermarking is not stand-alone. It, as one of a triad of technologies (the other two being encryption and digital signatures) that together can offer a reasonable level of copyright protection at a reasonable cost. Because of the many protection and watermarking options available, addressing an application is not a simple matter.

18. REFERENCES

1. Digital Watermarking and Stenography: Fundamentals and Techniques By Frank.Y.Shih2. Digital Watermarking and Stenography By Ingemar J.Cox, Matthew Miller, Jeffrey Bloomer 3. Robust Image Watermarking In The Spatial Domain By N.Nikolaidis & I. Pitas