Top2.1 Motivation And Goals
The increase in computational power and the proliferation of the Internet has facilitated the production and distribution of unauthorized copies of multimedia information. As a result, the problem of copyright protection has attracted the interest of the worldwide scientific and the business communities. The most promising solution seems to be the watermarking process where the original data is marked with ownership information hidden in an imperceptible manner in the original signal. Understanding of the human perception processes is the key to successful watermarking. Typical properties of a successful watermarking scheme includes (Cox et al., 2002)
- a.
The watermark should introduce no perceptual distortion.
- b.
The watermark should be embedded into the host signal, rather than into an added header of that signal.
- c.
The watermark should be hard to remove, or even detect without the prior knowledge of the watermarking scheme and the watermark sequence.
- d.
The watermark should be self-clocking, which also know as synchronization problem.
- e.
The watermark should be readily extracted to completely characterize the copyright owner.
The motivation of this book is to exploit the fundamental issues of digital watermarking and provide new solutions. We focus our research on the most important two key components of a watermarking system, namely psychoacoustic modeling and perfect synchronization. The former component makes the embedded watermarks inaudible while the latter makes recovery of embedded watermarks possible.
Top2.2 Watermark Applications
The applications of digital watermarking include but not limited to broadcast monitoring, owner identification, proof of ownership, transaction tracking, content authentication, copy control and device control (Cox et al., 2002).
2.2.1. Broadcast Monitoring
Some organizations and individuals like advertisers, performers and owners of copyrighted works are interested in broadcast monitoring. For advertisers, they want to make sure that they receive all the air time they paid for radio/TV station. For performers, they would like to collect the royalties from radio or TV stations when broadcasting their works. For owners of copyrighted works, they want to make sure their works are not illegally re-broadcasted by other unauthorized stations.
Although they could have a human to monitor the broadcast by watching, listening or recording the broadcast, it is expensive and error prone. Watermarks however, can be embedded to the content before broadcasting. Computer systems can then be used to monitor broadcasting by detecting the existence of watermarks from the broadcasted content.
2.2.2. Owner Identification
Copyright information on an image is usually printed on the original work by a texture copyright notice, which could be aesthetically unattractive and may cover a portion of the image. For other media like music, such copyright information can only be displayed on the physical media (CD, tape), which makes the owner identification hard to maintain when audio is transmitted over the internet. Watermark technology could be used to embed such owner identification into media files imperceptibly before the works get distributed. The watermarks should be robust enough to survive the channel noise, possible signal processing and even malicious attacks. For the audio case, the distributed audio file may undergo compression / de-compression, up or down sampling, AD / DA conversion. The copyright information embedded by watermarks can still identify the ownership after those possible processing.