DIGITAL WATERMARKING

Sejal Visawadia

Watermark

“ Watermarking can be considered as a special technique

of steganography where one message is embedded in another and the two messages are related to each other in some way. “

Example :-

The presence of specific patterns in currency notes which are visible only when the note is held to light is a well known example for watermark.

What is Watermarking?

Example of a conventional watermark

Courtesy of Blue Spike, Inc.

Digital Watermark

“ Digital watermarking is similar to watermarking physical objects, except that the watermarking technique is used for digital content instead of physical objects.”

Digital Watermark (Cont..)In digital watermarking a low-energy

signal is imperceptibly embedded in another signal. The low-energy signal is called watermark.

The main signal in which the watermark is embedded is referred to as cover signal since it covers the watermark.

An entity called watermark key used for embedding and detecting watermark signal

Watermark key is private

Behind The Technology

Sending Side …

Watermark Embedding process Water mark Original message Key Water marked image

Behind The Technology

Watermark retrieval process Water marked image KeyConfidential message

Receiving Side …

The Overall SystemThe Technology

Roars…

Importance Of Digital Watermarking

©Copyright Information©On-line music industry©News gathering using digital

cameras

Types of Digital Watermarking

Robust & Fragile Watermarking

Visible & Invisible Watermarking

Public & Private Watermarking Asymmetric & Symmetric

Watermarking Steganograhic & Non-

Steganographic watermarking

Robust & Fragile Watermarking

Robust Watermarking:-Modification of watermarked content will not affect watermark

Fragile Watermarking:-Watermark get destroyed when watermarked content is modified or tampered with

Visible & Invisible Watermarking

On Visible watermarking, contents are visible

Visible & Invisible Watermarking (Cont..) Invisible watermarking are not

viewed on just looking

Public & Private Watermarking• Public Watermarking Users of content are authorized to

detect watermark

• Private Watermarking Users not authorized to detect

watermark

Asymmetric & Symmetric watermarking

In Asymmetric watermarking different keys used for embedding and detecting watermark

Asymmetric & Symmetric watermarking (Cont..)

In symmetric watermarking same keys are used for embedding and detecting watermarks

Steganographic & Non-Steganographic Watermarking

Steganographic Watermarking User unaware of the presence of a

watermark eg:-Used in finger printing

applicationsNon-Steganographic WM:- User aware of the presence of a

watermark.

e.g.:-User to detect piracy

Digital Watermarking Techniques

LSB WatermarkingColor Separation TechniqueBit Stream WatermarkingWord Space Coding, Line Space

Coding &Character Coding

LSB Watermarking

Lower order bits of selected pixels in the image are used to store watermarks

Replacing lower order bits of each pixel with higher order bit of different image

Color Separation Technique

Watermark appears only in one of the color bands

Used to watermark in still imagesCan be extended to moving

images

Bit Stream Watermarking

Used in audio watermarking

Data is directly inserted into compressed audio files

Word Space Coding, Line Space Coding & Character Coding

Used for watermarking in text documents

In word space coding, the spaces between words are altered to embed watermark code. In line space coding the space between the lines are altered and in character coding some of the characters are imperceptibly modified (i.e., made larger, serifs enhanced, etc).

Applications of Digital Watermarking

Copy ProtectionContent AuthenticationCopyright ProtectionMetadata Tagging

Copy Protection

It limits the access to copyrighted material and inhibit the copy process

Content Authentication

Robust watermarks are used in this area

Example:-A photographic information that may be presented as evidence in court. Since digital images can be easily manipulated, there is a need to provide proof that an image has not been altered.

Content Authentication

Copyright Protection

One of the main application

Embedding watermarks in digital photographs

Metadata Tagging

Watermarks convey object specific information to users of the object.

Used to attach patient identification data to medical images, or to highlight regions of diagnostic significance.

Attacks to Digital Watermarking

Stirmark Mosaic Attack

Stirmark

It is tool developed to test the robustness of image marking system

Stirmark is commonly produced by printers and scanners

IBM researchers have recently announced a technique that defeats the stir mark attack.

Detects and measures the geometric distortions in images, and removes the distortion to restore image geometry

Stirmark Example

Mosaic Attack

Use of a web crawlerDividing into sub images with

rendition instructionsBrowser will be rearranging the sub

images to appear as the originalSub images will be sufficiently small

that no single image on its own will contain a recognizable mark.

Mosaic Attack Example

ConclusionDRM systems and content management are

important for protection of rights of digital multimedia creations that are distributed on the Internet. Digital watermarking is an effective technique for embedding rights information in digital multimedia data.

Digital watermark technology can be used in consumer electronic devices like digital still camera, digital video camera, DVD players, MP3 players, etc., for various applications like providing controlled access, preventing illegal replication and watermark embedding

Conclusion (Contd..)

Digital information can easily be disseminated and copied via global networks.

The future of digital watermarking relies on setting standards and creating applications so that creators of digital content can easily implement it.

THANK YOU