Digital Watermarking1.Introduction and history2. Terminologies3. Framework4. Techniques/Types5.Requirements6. Limitations7. Applications
1.1 What is digitalwatermarking..??a. Digital watermarking is the process ofembedding “information” into a digital media withoutcompromising the media’s value in a way that it isdifficult to remove.b. The term ‘watermark’watermark’ was introduced near the endof the 18th century. It was probably given because themarks resemble the effects of water on paper.
1.2 History in briefa. Was used in ancient Italy for indicating the paperbrands and name of mills.b. In 18thcentury to prevent money counter feting.c. The first example of a similar technology was doneby Emil Hembrooke in 1954 for identifying musicworks.
2. Terminologiesa. Steganographyb. Watermarkingc. Data hiding and data embeddingd. Copy protectione. Copyright protection
a. steganography•Steganography is an art ,science ,study, workof communicating in a way which hides a secretmessage in the main information.• Steganography methods rely generally on theassumption that the existence of the covert data isunknown to unauthorized parties and are mainlyused in secret point-to-point communicationbetween trusting parties.
b. Watermarking•Watermarking as opposed to steganography – inan ideal world can resists attacks. Thus, even if theexistence of the hidden information is known, itshould be difficult for an attacker to remove theembedded watermark, even if the algorithmicprinciple is known.
d. Copy protection•Copy protection attempts to find ways, whichlimits the access to copyrighted material and/orinhibit the copy process itself.
d. Copyright protection•Copyright protection inserts copyrightinformation into the digital object without the lossof quality. Whenever the copyright of a digitalobject is in question, this information is extracted toidentify the rightful owner.
3.Framewrok• Watermarking is the process that embedsdata called ‘watermark’ into a media such thatwatermark can be detected or extracted laterto make an assertion about the media. Forexample, digital watermarking technique forimages is to add a visible seal to the existingimage.
5.Watermarking techniquesa. According to the working domainb. According to the type of documentc. According to the human perceptiond. According to the application
a. Working domaina.1 spatial domain• Is applied to graphic images and text.• Slightly modifies the pixels of one or two randomlyselected subsets of an image.(generally the lower bits).
a.2 Frequency domain• also called transform domain.• Values of certain frequencies(normally low) arealtered from their original.
Some other techniques• Text line, word or character shifting.• Boundary modifications.• Least significant bit alterations.
5. Digital watermarking -Requirements• The watermark should exhibit certain characteristics.These include that the watermark is difficult tonotice, survives common distortion, resists maliciousattacks, carry many bits of information, can coexistwith other watermarks, and requires littlecomputation to insert or detect.
6.Technically• Fidelity(imperceptibility)• Robustness• Fragility• Modification and multiple watermarks
Attacks on the watermarksThe attacks on the digital watermarking can broadlybe classified in two types:• Attacks on the signal.• Cryptographic attacks.
Attacks on signal• The majority of the attacks are related to thewatermark signal itself .• They intend to remove the mark, or somehow maskit.• These techniques can rely on the structure of theembedding algorithm to know where and how thewatermark was incrusted.
Cryptographic Attacks• Some attacks try not to access the watermark, but tomodify its interpretation.• This is quite general applicability and possesses theinitially remarkable property that a marked image forexample can be unmarked and yet still rendered pixelfor pixel in exactly the same way as the marked imageby a standard browser.
7.Applications• Signature• Fingerprinting• Broadcast and internet monitoring• Authentication and integrity• Copy and copyright protection• Covert communication