Digital watermarking

CONTENTSBackgroundTerminology CharacteristicsApplicationsTechniquesReferences

Information Hiding

Information Hiding…..started with

Steganography (art of hidden writing):The art and science of writing hidden messages in such a way that no one apart from the intended recipient knows of the existence of the message. The existence of information is secret.

What is a watermark ?What is a watermark ? A distinguishing

mark impressed on paper during manufacture; visible when paper is held up to the light (e.g. $ Bill)

What is a watermark ?

Digital Watermarking: Application of Information hiding (Hiding Watermarks in digital Media, such as images,audio file)

Digital Watermarking is a process of embedding

digital signals or pattern into a multimedia object without affecting in any way the quality of the original file.

CHARACTERISTICS Transparency: watermark is not detectable

Robustness: survives digital processing (e.g., compression) and malicious analytical attacks.

Efficiency: low cost implementation using minimal resources

Independence: of both the type and format of multimedia data (e.g., music, speech, video, sample rates, coding scheme, ...)

ApplicationsCopyright Protecton:To prove the ownershipof digital media

Eg. Cut paste of images

Hidden Watermarks represent the copyright information

Applications

Tamper proofing: To find out if data was tampered.

Eg. Change meaning of images

Hidden Watermarks track change in meaning

Applications

Quality Assessment: Degradation of Visual Quality

Loss of Visual Quality

Hidden Watermarks track change in visual quality

Watermarking ProcessData (D), Watermark (W), Stego Key (K),

Watermarked Data (Dw) Embed (D, W, K) = Dw Extract (Dw) = W’ and compare with W

Figure 2 shows the basic scheme of the watermarks embedding systems.

Inputs to the scheme are the watermark, the cover data and an optional public or secret key. The output are watermarked data. The key is used to enforce security.

Figure 2: Watermark embedding scheme

Watermarking Process

Watermarking ProcessFigure 3 shows the basic scheme for watermark recovery system.

Figure 3: Watermark recovery scheme

Inputs to the scheme are the watermarked data, the secret or public key and, depending on the method, the original data and/or the original watermark. The output is the recovered watermarked W or some kind of confidence measure indicating how likely it is for the given watermark at the input to be present in the data under inspection.

TYPES TYPES OFOF WATERMARKING SCHEMES WATERMARKING SCHEMES

Private (non-blind) watermarkingPrivate (non-blind) watermarking systems use the original cover-data to extract the watermark from stego-data and use original cover-data to determine where the watermark is.

Semi-private (semi-blind) watermarkingSemi-private (semi-blind) watermarking does not use the original cover-data for detection, but tries to answer the same question. (Potential application of blind and semi-blind watermarking is for evidence in court ownership,....)

Extract using { K, W}

Public (blind) watermarkingPublic (blind) watermarking - neither cover-data nor embedded watermarks are required for extraction - this is the most challenging problem.

Extract using {K}

Extract using {D, K, W}

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.•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.

SecurityIn case the key used during watermark is lost

anyone can read the watermark and remove it.

In case the watermark is public, it can be encoded and copyright information is lost.

Referenceshttp://en.wikipedia.org/wiki/Steganography

http://en.wikipedia.org/wiki/Digital_watermark

http://www.cypak.com/pictures/med/Cypak