Digital Watermarking Ppt

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DIGITAL WATERMARKING

Digital Watermarking

Introduction and history Terminologies Framework Techniques/Types Reuirements

Limitations Applications

What is digital watermarking..??

Digital watermarking is the process of embedding “information” into a digital media without compromising the media’s value in a way that it is difficult to remove.

The term ‘watermark’watermark’ was introduced near the end of the 18th century. It was probably given because the marks resemble the effects of water on paper.

History in brief… Was used in ancient Italy for indicating the paper brands and name of mills. In 18th century to prevent money counterfeting. The first example of a similar technology was done by Emil Hembrooke in 1954 for identifying music works. Later it was used by Komatsu and Tominaga in 1988.

Terminologies… Steganography Watermarking Data hiding and data embedding Copy protection Copyright protection

Terminologies… Steganography-is an art,science,study, work of communicating in a waywhich hides a secret message in the main information.

Steganography methods rely generally on the assumption that the existence of the covert data is unknown to unauthorized parties and are mainly used in secret point-to-point communication between trusting parties.

Terminologies… Watermarking- as opposed to

steganography – in an ideal world can resists attacks. Thus, even if the existence of the hidden information is known, it should be difficult for an attacker to remove the embedded watermark, even if the algorithmic principle is known.

Terminologies… Copy protection- attempts to find ways, which limits the access to copyrighted material and/or inhibit the copy process itself. 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.

Framewrok

Watermarking is the process that embeds data called ‘watermark’ into a media such that watermark can be detected or extracted later to make an assertion about the media. For example, digital watermarking technique for images is to add a visible seal to the existing image.

A general watermarking system…

Watermarking techniques… According to the working domain According to the type of document According to the human

perception According to the application

Spatial domain Is applied to graphic images and

text. Slightly modifies the pixels of one or

two randomly selected subsets of an image.(generally the lower bits).

However, not reliable when subjected to normal media operations such as filtering or lossy compression.

Frequency domain also called transform domain. Values of certain

frequencies(normally low) are altered from their original.

The watermark is applied to the whole image so as not to be removed during a cropping operation and also to make its verification difficult.

Visible and Invisible watermarking Visible watermark is a secondary

translucent overlaid into the primary image

The invisible-robust watermark is embedded in such a way that alternations made to the pixel value are perceptually not noticed .

The invisible-fragile watermark is embedded in such a way that any manipulation or modification of the image would alter or destroy the watermark.

Fragile watermarking technique A watermark is said to be fragile if

the watermark hidden within the host signal is destroyed as soon as the watermarked signal undergoes any manipulation.

When a fragile watermark is present in a signal, we can infer, with a high probability, that the signal has not been altered.

Robust watermarking Robust watermarks are those which

can survive signal manipulations. Can withstand mallicious attacks

and signal processing too. Thus recommended for those

media which need to undergo during lossy compressions

Some other techniques Text line,word or charcter shifting.

Boundary modifications. Least significant bit alterations.

Digital watermarking - Requirements

The watermark should exibit certain characterstics.These include that the watermark is difficult to notice, survives common distortion,resists malicious attacks, carry many bits of information, can coexist with otherwatermarks, and requires little computation to insert or detect.

Technically… Fidelity(imperceptibility)

Robustness

Fragility

Modification and multiple watermarks

Attacks on the watermarks The attacks on the digital

watermarking can broadly be classified in two types:

Attacks on the signal. Cryptographic attacks.

Attacks on signal The majority of the attacks are

related to the watermark signal itself .

They intend to remove the mark, or somehow mask it.

These techniques can rely on the structure of the embedding algorithm to know where and how the watermark was incrusted.

Cryptolographics Attacks Some attacks try not to access the

watermark, but to modify its interpretation.

This is quite general applicability and possesses the initially remarkable property that a marked image for example can be unmarked and yet still rendered pixel for pixel in exactly the same way as the marked image by a standard browser.

Applications Signature Fingerprinting Broadcast and internet monitoring Autentication and integrity Copy and copyright protection Covert communication

By - Priyanka Raj charan Cs 5b 0114cs081089

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