Digital Watermarking Simg-786 Advanced Digital Image Processing Team 1

What is digital watermarking? Digital watermarking is the process that embeds data called a watermark or digital signature or tag or label into a multimedia object such that watermark can be detected or extracted later to make an assertion about object. It is widely used in Copyright Marking

General Framework for watermarking E(I, S) = J D(J, R) = S’

Different types of watermarking Visible: watermark is a secondary translucent overlaid into primary image. Invisible: watermark is perceptually not noticed and it can be recovered only with appropriate decoding mechanism. Invisible-fragile: any modification of the image will destroy the watermark.

Application of Digital Watermark Visible watermarks: - for enhanced copyright protection. Images will be used commercially (e.g. imprinting coffee mugs) without payment of royalties. - used to indicate ownership originals (e.g. library manuscript). Invisible Robust watermarks: - detect misappropriated images. - as evidence of ownership. - identification Invisible Fragile Watermarks - detect alternation of images stored in a digital library (e.g. human fingerprints).

Attacks on Watermarks Lossy Compression Geometric Distortions (rotation, translation, scaling and cropping) Resampling Requantization Linear and non-linear filtering Color reduction Addition of noise Printing and Rescanning Rewatermarking And more …

Desired Characteristics of Invisible Robust Watermarks Neither be noticeable to viewer nor degrade the quality of content. Robust, resistant to various intentional tampering solely intended to remove the watermark. Watermark should unambiguously identify the owner Minimum the amount of pixel modification

Potential Market of Digital Watermark Web-based vendors selling software, DVD, CD, video, music Medical Imaging application Legal documents authentication

Applications of Digital Watermarking Intellectual Properties Protection Embed visible, invisible or both trademarks, copyright statement on computer software, digital images, videos, documents. Users won’t be able to steal the owner’s property, the embedded watermark will prove the ownership. Combined with data encryption technique, more restrictions can be imposed to authorized users

Robustness testing of image watermarking StirMark is a generic tool for simple robustness testing of image watermarking algorithms. It can be applied to photographic digital images and it will distort the watermark of too simplistic marking techniques such that the embedded watermark cannot any more be detected and decoded from the result image. It is Free! StirMark is freely available under the GNU General Public License.

StirMark introduces a practically unnoticeable quality loss in the image if it is applied only once. However after a few iterated applications of the algorithm, the image degradation becomes soon very noticeable. Processes like scaling, rotation, JPEG compression, shearing and warping.

Some Benchmark examples: