This PPT presentation is based on the topic Digital Watermarking
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DEFINITION OF WATERMARKING
PURPOSE OF DIGITAL WATERMARLING
ENCODING PROCESS OF WATERMARK TO OBJECT
DECODING PROCESS OF WATERMARK FROM AN OBJECT
TYPES OF DIGITAL WATERMARKING
TYPES OF ATTACKS
WHAT IS WATERMARK: Watermark is a digital signal or pattern inserted into a digital image ,or audio or vedio or software .
WHAT IS DIGITAL WATERMARKING :
Digital Watermarking is the process that embeds data called a watermark into a multimedia object such that watermark can be detected or extracted later to make an asertation about the object .
At the time of inserting a watermark into image some additional information is kept. This information includes identifiers of the owner, recipient and/or distributor, transaction dates, serial numbers, etc. which play a crucial role in adding value to watermarking products.
PURPOSE OF DIGITAL WATERMARKING :
Watermarks added to digital content serve a variety of purposes. The following list details six purposes of digital watermarking .
• Ownership Assertion – to establish ownership of the content (i.e. image)
• Fingerprinting – to avoid unauthorized duplication and distribution of publicly available multimedia content
• 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
• Content labeling – bits embedded into the data that gives further information about the content such as a graphic image with time and place information
• Usage control – added to limit the number of copies created whereas the watermarks are modified by the hardware and at some point would not create any more copies (i.e. DVD)
• Content protection – content stamped with a visible watermark that is very difficult to remove so that it can be publicly and freely distributed
ENCODING OF A WATERMARK INTO AN IMAGE :
Let us denote an image by I, a signature by S=s1,s2,s3….. and 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 I1,matheamatically
It should be noted that the signature S may be dependent on image I.In such cases,the encoding process Described by Eq1 still holds.Following figure illustraits the encoding process.
DECODING PROCESS OF AN WATERMARK FROM AN OBJECT :
A 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 S’ 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.
The extracted signature S’ will then be compared with the owner signature sequence by a comparator function C and a binary output decision generated. It is 1 if there is match and 0 otherwise .
Where C is the correlator,x=C(S’,S). C 8 is the correlation of two signatures and 0 is certain thresold. Without lose of generality,watermarking scheme can be treated as a three_tuple (E,D,C) .Following figures demonstraite the decoder and compator .
TYPES OF WATERMARKING :
1. Image watermarking
2. Video watermarking
3. Audio watermarking
4. Text watermarking
IMSGE WATERMARKING :
according to human perception image watermarking is divided into two types
Visible watermark is a secondary translucent overlaid into the primary image. The watermark appears visible to a casual viewer on a careful inspection.
2.INVISIBLE WATERMARK :
The invisible watermark is embeded in such a way that alternations made to the pixel value is perceptually not noticed and it can be recovered only with appropriate decoding mechanism. For the pixels the lower bits of the byte are changed .
(WATERMARKED IMAGE WITH 90% QUALITY FACTOR)
The process of watermarking the sequence of video frames’’ is called video watermarking.
The process of embedding information into audio can be termed as audio watermarking.
TEXT WATERMARKING :
The process of embedding/hiding data in text can be termed as ``text watermarking''
APLICATION OF VISIBLE WATERMARK :
Visible watermarks can be used in following cases:
_ Visible watermarking for enhanced copyright protection. In such situations, where images are made available through Internet and the content owner is concerned that the images will be used commercially (e.g. imprinting coffee mugs) without payment of royalties.
Here the content owner desires an ownership mark, that is visually apparent, but which does not prevent image being used for other purposes (e.g. scholarly research).
_ Visible watermarking used to indicate ownership originals.
In this case images are made available through the Internet and the content owner desires to indicate the ownership of the underlying materials (library manuscript), so an observer might be encouraged to patronize the institutions that own the material.
Following are the applications of invisible fragile watermarks.
_ Invisible watermarking for a trustworthy camera. In this scenario, images are captured with a digital camera for later inclusion in news articles. Here, it is the
Desire of a news agency to verify that an image is true to the original capture and has not been edited to falsify a scene. In this case, an invisible watermark is
embedded at capture time; its presence at the time of publication is intended to indicate that the image has not been attended since it was captured.
In case of audio watermarking time and frequency masking properties of the human ear is used to cancel the watermark and make it inaudible. So that the user can not distinguish the difference between the original audio and watermarked audio. But it is little difficult to synchronize the watermark and watermarked audio file.but now many techineques are coming to overcome this problem.
HARDWARE /SOFTWATE WATERMARKING :
In case of hardware to achive a watermark the Boolean equivalence s can be exploited to yield instances that use different types of gates.
In case of software it can also be protected not only by finding the equivalences between instructions ,variable names, or memory address but also by altering the order of noncritical instructions. All this can be accomplished compiler level.
ATTACKS ON DIGITAL WATERMARKING:
• Active Attacks – hacker tries to remove the watermark or make it undetectable. An example is to crop it out.
• Passive Attacks – hacker tries to determine whether there is a watermark and identify it. However, no damage or removal is done.
• Collusion Attacks – hacker uses several copies of one piece of media, each with a different watermark, to construct a copy with no watermark.
• Forgery Attacks – hacker tries to embed a valid watermark of their own rather than remove one.
• Decorative Attacks – hacker applies some distorted transformation uniformly over the object in order to degrade the watermark so that it becomes undetectable/unreadable.
The watermarking research is progressing very fast and numerous researcher from various fields are focussing to develop some workable scheme. Different companies also working to get commercial products. We hope some commercial and effective schemes will be available in the future.