21-06-2013, 12:51 PM
Hardware Assisted Watermarking for Multimedia
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Abstract
Digital media offer several distinct advantages over analog media, such as high quality, ease of editing, and ease of processing
operations such as compression and high fidelity copying. Digital data is commonly available through digital TV broadcast, CD,
DVD, and computing devices such as personal computers. The ease by which a digital media object can be duplicated and distributed
has led to the need for effective digital rights management tools. Digital watermarking is one such tool.Watermarking is the
process of embedding extra data called a watermark into a multimedia object, like image, audio, or video, such that the watermark
can later be detected or extracted in order to make an assertion regarding the object. During the last decade, numerous software
based watermarking schemes have appeared in the literature and watermarking research has attained a certain degree of maturity.
But hardware based watermarking systems have evolved more recently only and they are still at their infancy. The goal of hardware
assisted watermarking is to achieve low power usage, real-time performance, reliability, and ease of integration with existing
consumer electronic devices. In this paper, we survey the hardware assisted solutions proposed in the literature for watermarking
of multimedia objects. The survey is preceded by an introduction to the background issues involved in digital watermarking.
Introduction
Electronic watermarking was invented in 1954 by Emil Hembrooke of the Muzac Corporation (1). A vast research
community involving experts from computer science, cryptography, signal processing, and communications has come
together in the last decade to develop watermarks suitable for various applications. Digital watermarking is intended
by its developers as the solution to the requirement of providing value-added protection on top of data encryption
and scrambling for content protection. Like any other technology under development, digital watermarking raises a
number of essential questions (1; 2; 3). In this paper we will attempt to address some of these questions followed by a
detailed discussion on hardware based solutions for image and video watermarking available in the current literature.
General Framework, Types, and Applications ofWatermarking
In general, watermarking is the process that embeds data called a watermark into a multimedia object such that it
can be detected or extracted later to make an assertion about the object. The object may be an image or audio or video.
A simple example of a digital watermark would be a visible “seal” placed over an image to identify the copyright.
However the watermark might contain additional information including the identity of the purchaser of a particular
copy of the material. In this section, we introduce the general framework of watermarking, discuss different types of
watermarking and their applications.
General Framework
As demonstrated in Fig. 1, any watermarking scheme consists of several distinct parts (12; 7; 19; 20; 21): the
watermark, the encoder, the decoder and comparator. The watermark is usually an image in the case of a visible
watermarking scheme. In the case of invisible watermarking, it can be a binary image, random or pseudorandom
number. Each owner has a unique watermark or an owner can also place different watermarks in different objects. The
insertion algorithm incorporates the watermark into the object. The verification algorithm authenticates the object,
determining both the owner and the integrity of the object.
Based on Human Perception
Based on human perception, digital watermarks can be divided into visible and invisible types (26; 14; 7; 12). A
visible watermark is a secondary translucent image overlaid into a primary image. The watermark appears visible
to a viewer only on careful inspection. On the other hand, the invisible watermark is completely imperceptible. The
invisible-robust watermark is embedded in such a way that alterations made to the pixel value are perceptually not
noticeable and can be recovered only with the 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.
There are multiple watermarking algorithms presented in the literature such as (29; 30; 31; 32) that serve different
purposes. For example, the dual watermark in (31) is a combination of a visible and an invisible-fragile watermark.
An invisible robust private watermarking scheme requires the original or reference image for watermark detection
whereas public watermarks do not (12; 22). The class of invisible robust watermarking schemes that can be attacked
by creating a “counterfeit original” is called invertible.
Attacks onWatermarks and Watermarking Systems and Benchmarks
A watermarked object is likely to be subjected to certain manipulative processes before it reaches the receiver.
Common signal processing functions such as analog-to-digital conversion, digital-to-analog conversion, sampling,
quantization, requantization, dithering, recompression, linear and nonlinear filtering, low-pass and high-pass filtering,
addition of Gaussian and non Gaussian noise are common manipulations. An attack is any processing that impairs or
misleads the watermark detector (4). The performance of a watermarking algorithm against these attacks reflects its
quality (42; 13; 14; 5; 43; 44; 45; 46). Similarly, it is anticipated that an embedded system realization of watermarking
can face several physical attacks similar to the ones suggested for cryptography in the literature (47).
The requirements for fulfilling desired characteristics and the requirements for performance against attacks are
mutually conflicting. There are many watermarking algorithms proposed in the current literature and a metric has
been developed for their comparison so that the user can make a decision to use one of the algorithms that best suits
his need. The benchmarks essentially combine many attacks in a unified framework and allow the user to test the
watermarking system for its applicability. There are several benchmarks available, such as Stirmark, (11; 48), Unzign
(49), Checkmark (50; 51), and Certimark (4). In this section, we provide a broad discussion on the various attacks and
available benchmarks.
An Invisible-Robust Watermarking Module
A real-time watermarking embedder-detector for broadcast monitoring in the framework of a VLIW DSP processor
is presented in (70; 71; 76; 77). The authors present the European Esprit project VIVA that aims at intellectual property
protection of professional TV broadcast surveillance systems. In the insertion procedure, pseudo-random numbers are
added to the incoming video stream based on the luminance value of each frame and the watermark detection is based
on the calculation of correlation values.
Conclusions
In this paper, we have considered various aspects of digital watermarking.We have provided a broad perspective of
watermarking including its basic theory, its types, technical requirements, and various other issues. We have surveyed
watermarking chips proposed in the current literature. The need of low power, low cost, high performance real time
operation, and high security with watermarking done at the data acquisition stage drives the VLSI implementation
of the watermarking schemes. The VLSI implementation is still at a relatively early stage of development and a lot
more research is needed before a complete VLSI architecture with all the desired characteristics can be obtained.
The collaborative work of the VLSI, signal processing, and watermarking communities is required. In particular,
with sufficient feedback from the VLSI community, the watermarking algorithms should be designed so that their
hardware implementation becomes feasible. Sufficient attention should be provided for the design of ultra low power
watermarking chips.