DIGITAL WATERMAKING (DWM)

INTRODUCTION

Digital documents i.e. documents created in digital media are having certain
advantages like-

· Efficient storage,duplication,manipulation and transmission.

· Copying without loss.

Such digital documents consists of images,audio clips and videos etc.But due
to some delimits of digital documents,they become inefficient to use.These
delimits are as follows

· Illegal copying

· Falsification(duplication)

· No copyright protection

· No ownership identification

The large use of networked multimedia system has created the need
of “Copyright Protection”for different digital medium as images,audio clips,
videos etc.The term “Copyright Protection” involves the authentification of
ownership and identification of illegal copies of digital media.Though digital
media provides various efficient facillities like distribution,reproduction and
manipulation of images,audio clips and videos,they increases illegal copying
of digital media.The solution for this problem is to add the visible or invisible structure
to digital media which is to be protected from copyright. These structures are
known as “Digital Watermarks” and the process of adding digital watermarks
to digital media is known as “Digital Watermarking”.

Digital watermarking is created by inserting a digital signal or pattern into digital content. Digital watermarking is nothing but process of conveying information by imperceptiblly embedding it into digital media.The purpose of embedding the information depends upon application and need of user of digital media. Digital watermarking provides the solution for difficult problem of providing guarentee to organiser and consumer of digital content about their legal rights.Copyright protection for multimedia information is nothing but a golden key for multimedia industry.Digital watermarking is a technology that opens a new door for authors,producers,publishers and service providers for protection of their rights and interest in multimedia documents.

There are various techniques for prevention of illegal copying.They are described as follows

1. Encryption methods which includes use of public and private keys to encode the data so that image can decoded only with required key.
2. Site security methods which includes use of firewalls to access the data.
3. Using Thumbnail images.and the most popular and important
4. Digital watermarking which includes robust labelling of an image with Information which is to be prevent from illegal copying and also use of image checksum or other techniques to detect manipulation of image data.In general sense,Digital Watermarking means “Author Signature”.

Digital watermarking is the process of encoding hidden copyright info-

rmation in an image by making small modifications in it’s pixel content.In this case watermarking doesn’t restrict the accessing image information. The important function of watermarking is to remain present in data for proof of ownership.The use of digital watermarking is not restricted upto copyright protection.Digital watermarking can also be used for owner identification to identify content of owner,fingerprinting to identify buyer of content,broadcast monitoring and authentification to determine whether the data is changed from it’s original form or not finally the actual meaning of Digital watermarking technique is come to know from following three point of views
1. Work=>A specific song,video,picture or specific copy of such.
2. Content=>Set of all possible works.
3. Watermarking=>The practise of imperceptiblly altering a work to embed
a message about that work.

The watermarking solution promise to protect your images by inserting text information and then tracking the images.Digital watermarking distinguishes digital copies and mark documents with owner’s ID.There are many reasons to embed information in digital content using digital watermarking. The internet boom is one of the reasons.It has become very easy to connect to internet from home computers to obtain or provide various information using World Wide Web(WWW). All information handled on internet is in digital form.Such digital content can be copy such that new file is indistinguishable from original one.Then content can be reproduce in large quantities. .Digital watermarking protecting such illegal copying.A watermark discourage piracy and determines criminals of making illegal copies of digital media.

WHAT IS AND WHY TO USE DWM?

2.1What is it?

Digital watermarking is an adaptation of the commonly used and well known paper watermarks to the digital world.Digital watermarking describes methods and technologies that allow to hide information.The hiding process has to be such that the modifications of the media are imperceptible.Digital watermarking is a technology for embedding various types of information in digital content.In general,information for protecting copyrights and providing the validity of data is embedded as watermark.Digital watermarking is relatively a new way of protecting intellectual property However,theories and technologies behind it are computer based steganography,cryptography,spread spectrum communications and noise theory.

2.2Why to use it?

First important application come into mind is copyright protection of digital media.It is easy to duplicate digital data exactly without quality loss.Similarto process in which artist signed their painting with a brush to claim theircopyrights,artist of today can watermark their work and hide some information say their name in the image.Hence,embedded watermark will allow to identify the owner of work.This concept is applicable to digital video and audio also.Especially,distribution of digital audio over internet in MP3 format is currently a big problem.Digital watermarking may be useful to setup controlledaudio distribution and provide efficient means for copyright protection,usuallyin collaboration with international registration bodies such as IDDN(InterDeposite Digital Number).In addition with copyright protection,Digital watermarking is playinga important role in many fields of applications such as broadcast monitoring,owner identification,transaction tracking,proof of ownership,fingerprinting, content authentification,copy control,device control.Digital watermarks can alsoserve as invisible labels and content link.For example,photo development labsmay insert a watermark into the picture to link the print to it’s negative.so, it isbecomes easy to find out negative of a print.All one has to do is to scan the printand extract the information from negative.In a completely different scenario,the digital watermarks may be used as a geometrical reference which may be useful for programs such as Optical Character Recognition(OCR) software.The embedded calibration watermark may improve the detection reliability of the OCR software since it allows the determination of translation,rotation and scaling.Digital watermarking also serves as a means of advertising within the digital media.For instance,the user may download and view a digital image,use a watermark reader to extract the digital signature,then acess a web based directory to find the company’s name and up-to-date address,phone number and web and e-mail address.Digital watermarks also serves the purposes of identifying quality and assuring authenticity.A graphic or audio file bearing digital watermark can inform the viewer or listener who owns to the item

PROPERTIES AND CLASSIFICATION OF DWMs

3.1Properties=>

For better activeness,watermark should be invisible within host media,statistically invisible to unauthorized removal,readily extracted by owner of image,robust to accidental and intended signal distortion like filtering,compression,resampling,retouching,crapping etc.For a digital watermark to be effective for ownership,it must be robust,recoverable from a document,should provide the original information embedded reliably and also removed by authorized users.

All these important properties of digital watermarks are described as-
1. Robustness=>The watermark should be robust such that it must be difficult to remove.The watermark should be robust to different attacks.The robustness describes whether watermark can be reliably detected after performing some media operations.
2. Perceptual transparency=>This property describes that whether watermark is visible or invisible to human sensor organ.Perceptible watermarks are visible to human while imperceptible are not.Imperceptible watermarks are such that content remains same after applying digital watermarking technique.
3. Security=>Security property describes that how easy to remove a watermark.This is generally reffered to as “attack” on watermarking.Attack refers to detection or modification of watermark.
4. Complexity=>This is important property which is to be consider in real time applications like video.Complexity property is concerned with amount of effort needed to extract or retrieve the watermark from content.
5. Capacity=>Capacity property of digital watermarks refers to amount of informatio that can be embedded within the content.The important point is that more data is used in watermark,watermark will become less robust.

In addition to these properties,watermarks are having some extra properties as unambiguity,tamper resistance,inseperable from the works and able to undergo some transformation as works.

3.2Classification=>

Digital watermarks are classified according to their applications.The watermarks are classified as perceptible watermarks and imperceptible watermarks,robust and fragile,public and private.This classification of watermarks are broadly described in following sections.

1. Perceptible watermarks and imperceptible watermarks=>

Perceptible watermarks are visible to human eye while imperceptible watermarks are invisible.The perceptible watermarks are useful for primary application i.e. for statement ownership or authorship.So for this reason it should be visible. .On the other hand imperceptible watermarks are useful for complex applications such as document identification in which content being watermarked must appear in unchanged form Examples of visible(perceptible) watermarks are logos on TV,IBM’s watermark and that of invisible(imperceptible) watermarks are ATT,NEC/MIT,UU etc.

Perceptible watermarks i.e. visible one are extension of the concept of logos.They are applicable to images only.These watermarks are embedded into image.They are applicable in maps,graphics and software user interface.Imperceptible watermarks i.e.invisible one remains hidden in the content.They can be detectrd only by authorized agency.These watermarks are useful for content or author authentication and for detecting unauthorized copier.

2. Robust watermarks and fragile watermarks=>

Robust or fragile is nothing but degree to which watermarks can withstand any modifications of any types caused due to the transmission or lossy

compression.Perceptible watermarks are more robust in nature than imperceptib-

le one.But meaning of this is not that imperceptible watermarks are fragile one.

Robust watermarks are those watermarks which are difficult to remove

from the object in which they are embedded.Fragile watermarks are those water-

marks which can be easily destroyed by any attempt to tamper with them.Fragile

watermarks are destroyed by data manipulation.

3. Private watermarks and public watermarks=>

Private watermarks requires atleast original data to recover watermark information Public watermarks requires neither original data nor embedded watermarks to recover watermark information.Private watermarks are also known as secure watermarks.To read or retrieve private watermark,it is necessary to have secret key.Public watermark can be read or retrieve by anyone using specialized algorithm.In this sense public watermarks are not secure.Public watermarks are useful for carrying IPR information.They are good alternatives to labels.

RELATIVE CONCEPTS AND ATTACKS

5.1 Relavent terms=>

Digital watermarking,steganography,information hiding,cryptography are closely related concepts.In each technique,a digital signal or pattern is inserted into,onto before or after digital document.There are some difference between working principle of these techniques and their meanings.

5.1.1 Information hiding=>

Information hiding is also called as ‘Data hiding’.The hiding is concerned with making information imperceptible or keeping it’s existence secrete.Information hiding means encompassing wide range of problems beyond that of embedding messages in content.Information hiding deals with communication security.It consists of encryption and traffic security.Encryption protects the content during distribution over an open network such as internet.The traffic security is related to concealing it’s sender,it’s receiver.Thus,here an attempt is made to have secrete communication between each two parties where existence is unknown to attacker.

5.1.2 Steganography=>

It is nothing but sub-discipline of information hiding.Here secrete information is hidden in harmless message,which is also known as cover message.steganography is used to avoid drawing suspictions to transmission of hidden message so as to remain undetected.The idea behind this is that to hide message in envolope or wrapper.In steganography,existence of hidden message in content is not known audience.

5.1.3 Cryptography=>

This technique is related with data protection.It is commonly used for protecting digital information.Once,data is decrypted,it can’t remain protected for long time i.e. there may be more chances of illegal copying of this data.So, there is great need of cryptography technique.Watermarking is special case of cryptography.Cryptography involves some suitable and complicated techniques so that no unauthorized user is allowed to access the data to protect.Authorisation of user is checked by certain keys or signature.

5.1.4 Watermarking=>

Watermarking is technology derived from steganography.It is also sub-discipline of information hiding.Watermarking is process of embedding secrete and robust idintifier inside audio,video content.The purpose of watermarking is to establish the copyright of content creator.In this sense watermarks are also known as the hidden copyright messages.watermarking secures the content,thus any attempt to modify the content can be easily detected.The watermarking can trace the path followed by content in distribution chain.This helps in tracing malicious users.

5.2 Attacks=>

Due to some reasons,there is need of adding,altering or removing false watermarks.Attacks on watermarks may be accidental or intentional.Accidenatal attcks may caused due to the standard image processing or due to the compression procedures.Intentional attacks includes cryptanalysis,steganalysis,image processing techniques or other attempts to overwrite or remove existing watermarks.

Following are the methods of attacks vary according to robustness and Perceptability.

5.2.1 Mosaic attack=>

Mosaic attack is the method in which pictures are displayed so as to confuse watermark searching program ,known as “Web Crawler”.Mosaic is created by subdividing the original image into randomly sized small images and displaying the resulting image on webpage.

5.2.2 Geometric attack=>

Geometric attack is related to geometric properties of data.It is concerned with images,documents and audio files.This attack is futher classified as-

Subtractive attack=>

It involves the attacker in the area of located watermark if imperceptible and then Removing the mark by cropping or digital editing.

Distortive attack=>

In this attack,attacker attempts to make some uniform distortive changes in the images such that mark become unrecognizable.

These two watermark attacks are usually performed on robust watermark.

5.2.3 Stirmark attack=>

Stirmark is generic tool developed for simple robustness techniques of image Marking algorithms and steganographic techniques.In it’s simplest version,stirmark simulates resampling process in which it introduces same kind of errors into an image to print it on high quality printer and scanning it again with high quality scanner.It includes minor geometric distortion.

This testing tool is an effective program to remove fairly robust watermarks in images and become a form of attack on it’s own.

5.2.4 Forgery attack=>

Forgery attack is also known as ‘Additive attack’ in some cases.Forgery attack include the attacker who can add his or her own watermark overlaying the original image and marking the content as their own.

5.2.5 Inversion attack=>

Inversion watermark render the watermark information ambiguous.Ihe idea behind the invesion attack that attacker who receives watermarked data can claim that data contains his watermark also by declaring part of data as his watermark.The attacker can easily generate the original data by substracting the claimed watermark.

5.2.6 Cryptanalysis=>

It is mostlly associated with cryptography.It is a method in which attacker attempts to find the decryption key for an encrypted pieces of information so that it can be made useful again.Attacker can remove licensing watermark that decrypts tha data ,attacker would use cryptanalysis to find decryption key so that data can use in decrtpted form free from it’s watermark.

ADVANTAGES AND DISADVANTAGES OF DWM

6.1 Advantages of digital watermarking=>

The field of digital watermarking is not restricted to digital images.This technique time and frequency masking properties of human ear to conceal the watermark and make it unaudible.There are some benefits of this technique as-

Benefits=>

· Uniquely identifies author of copyrighted works.

· Robust design of digital waetrmark withstand pirating attacks.

· Embedding watermark is easy.

· Implementation on PC platform is possible.

There are some military and civilian applications of digital watermarking also.

Military applications=>

· Intelligence activities.

· Traitor tracing.

· Image tampering detection.

Civilian applications=>

· Copyright protection of each digital media in hardcopy or on internet.

· Intelligent web browsers.

· Law enforcement for “chain of evidence”.

Some special watermarking technique uses color separation.So,watermarks appears in only one of the color bands.therefore,watermarks becomes strongly invisible.whenever,the colors are separated from printing then watermarks becones visible.This approach is advantageous to journaliststo inspect digital pictures from a photo stockhouse before buying an un-watermarked versions.

There is an important advantage of invisible fragile watermarks.With such invisible fragile watermarks,implementation of web based image authentication.This web based authentication includes watermark embedding and authentication system.In case of watermark embedding system,it is installed in server as application software that any authorized user who access to server can generate watermark image.The distribution can be done through any network as FTP,e-mail etc.Once,image is distributed to externally,client can get authentification web page to get verification of images.Digital watermarking techniques is having advantages as we seen earlier.

It also have some limits also.

6.2 Disadvantages of digital watermarking =>

Digital watermarking is recent research field,therefore it’s intrinsic limitations are not understood yet.The blind watermarking algorithm which is really robust is not in existence today. Another disadvantage is that owner can erase the watermark.By knowing the exact content of watermark and algorithms to enbed and retrieve it. It is always possible to make it unreadable without any significant degradation of the data.Again it is not clear that.if this drawback will be got around in future,in the meantime,the possibility of erasing the watermark or it’s part ,once it’s content is known must be taken into account when designing a copyright protection system. As a matter of fact,if any one is allow to read the watermark,then anyone can erase it by knowing the embedding algorithm.In some researches,the conclusion comes that not all watermarking techniques will be useful in resolving ownership disputes.Watermarking doesn’t prevent image copying as much as it simply makes copied images easier to track down and detect owners.