Watermarking Technology Ishani Vyas CS590 Winter 2008

Introduction Hiding information (data) with in digital audio, images and video files. Different way to hide the information  Digital Signature  Copyright Label  Digital watermark Digital watermarking - is the process that embeds data called a watermark into a multimedia object such that watermark can be detected or extracted later to make an assertion about the object. Object may be an image or audio or video.

Definition & Type of watermarking technology It is emerging field in computer science, cryptography, signal processing &communication. Visible Watermarking Visual patterns, like logos, which are inserted into or overlaid on images. Mainly apply on Images. Invisible Watermarking  Invisible –Robust is embed in such a way that alternations made to the pixel value is perceptually not noticed and it can be recovered only with appropriate decoding mechanism  The invisible-fragile watermark is embedded in such a way that any manipulation or modification of the image would alter or destroy the watermark. Dual Watermarking

Dual watermark is a combination of a visible and an invisible watermark. In this type of watermark an invisible watermark is used as a back up for the visible watermark as clear from the following diagram.

Information that can be included in the Watermark A serial number or pseudo random number sequenceserial Ownership identifiers Copyright messages Control signals Transaction dates Information about the creators of the work Bi-level or gray level images Text or other digital data formats.

Requirements of digital watermark Should convey as much information as possible Should be secret and accessible by authorized parties only Should withstand any signal processing and hostile attacks, i.e. robustness Should be imperceptible

Example of Image Watermarking

 For video two typical watermarking techniques used.  Spread Spectrum  DCT coefficients quantization

Watermarking in Video (MPEG) Pre- processing Motion Estimation DCTQuantization Variable Length Coding MPEG Video Output Input Video Example of standard MPEG encoder Variable Length Decoding MPEG Input Inverse Quantization IDCT Post Processing Output Video Example of standard MPEG decoder

Watermark Inserter Pre- processing Input Video Motion Estimation DCTQuantization Variable Length Coding Example of standard MPEG encoder with Watermark Inserter W E A M T B E R D M D A E R R K

MPEG Decoder with Watermark Detector Variable Length Decoding MPEG Input Inverse Quantization IDCT Post Processing Output Video W D A E T E R C M T A O R R K

Feature Summary  Watermarking can occur in DCT-based compressed video (MPEG1, MPEG2, MPEG4, H.264, WM9, other)

Watermarking Benchmarking: Benchmarking Software: – Unzign – StirMark – CheckMark – OptiMark