Digital media has replaced analog media in many applications within the last decade. This is mainly due to improved properties like simple noise-free transmission over general purpose channels, compact storage, perfect copying and simple editing. Further, the availability of the Internet as an open global network for the transmission of digital data accelerated the use of digital media. These first view advantages of digital media over analog media turn into disadvantages with respect to the protection of intellectual property rights and the trustworthiness of the content. Simple noise-free transmission of digital data (e. g., images, audio and video) via the Internet enables pirates to reach a huge market, while prosecution is difficult. Even worse, perfect copies are obtained easily and can be stored on CDs or DVDs.
In this paper on efficient watermarking algorithm is proposed for copyright protection of satellite images. A look-up table method in pixel domain that does not distort certain specific regions in the original images has been used. A watermark is embedded invisibly and irreversibly in host image without disturbing the vital area of ones interest.
The watermark is embedded in such a way that it can be easily extracted on production of the watermarking key.
INTRODUCTION
Digital watermarking is an adaptation of the commonly used and well-known paper watermarks to the digital world. Digital watermarking describes methods and technologies that allow hiding of information, for example a number or text, in digital media, such as images, video and audio. The embedding takes place by manipulating the content of the digital data that means the information is not embedded in the frame around the data.The first distinction that one needs to do in the study of watermarking for digital media is the notion of visible watermarks versus invisible ones. The first one are used to mark, obviously in a clearly detectable way, a digital image in order to give a general idea of what its look like while preventing any commercial use of that particular image. The purpose here is to forbid any unauthorized use of an image by adding an obvious identification key, which removes the images commercial value
On the other hand, invisible watermarks are used for content and/or author identification in order to be able to determine the origin of an image. They can also be used in unauthorized image’s copies detection either to prove ownership or to identify a costumer. The invisible scheme dose not intend to forbid any assess to the image but its purpose is to be able to tell weather a specified image has been used without the owner’s formal consent or if the image has been altered in any way.
The hiding process has to be such that the modifications of the media are imperceptible. For images this means that the modifications of the pixel values have to be invisible. Furthermore, the watermark has to be robust or fragile, depending on the application. With robustness we refer to the capability of the watermark to resist to manipulations of the media, such as lossy compression, scaling, and cropping, just to enumerate some. Fragility means that the watermark should not resist tampering, or only up to a certain extent. The watermarked information can directly control the digital recording device. The embedded key can represent a copy permission bit stream that is detected by recording device or using (viewing the CD or DVD) which then decide if the procedure should go on (allowed) or not(prohibited). A different application is related to copy-control. Several companies work on a watermarking system for copy control in the DVD environment. Fully functioning solutions exist already, however, for the moment they have not been entirely approved by the content producers and providers. Finally, this solution is also an efficient and simple way to prevent the use of illegal copies of software. It has a similar functionality as the anti-piracy device called "dongle", but is more compact (you can loose a dongle) and less expensive.
Broadcast Monitoring:
In order to help the automated identification of broadcasted programs, original watermarks can be inserted in any type of the data to be widely broadcasted on a network. It could assure that advertisers received the airtime they have paid for or make certain that musician’s property is not rebroadcast by pirate stations (or at least, if so, that can be detected)
Data Hiding (Covert Communications):-
The transmission of private data is probably one of the earliest applications of watermarking. As one would probably have understood, it consists of implementing a strategic message into an innocuous one in a way that would prevent any unauthorized person to detect it.
Medical Safety:
Embedding the date and patient’s name in medical images could increase the confidentiality of
medical information as well as the security
What is digital watermarking?
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The digital watermarking system essentially consists of a watermark embedder and a watermark detector . The watermark embedder inserts a watermark onto the cover signal and the watermark detector detects the presence of watermark signal. Note that an entity called watermark key is used during watermark embedded and extraction of watermarks.
The watermark key is private and known to only authorized parties and it ensures that only authorized parties can detect the watermark. The digital watermarking techniques should be resilient to both noise and security attacks
How it can be achieved?
In the spatial domain:-
The first watermarking scheme that was introduced, works directly in the spatial domain. By some Image analysis operations (e.g. Edge Detection), it is possible to get perceptual information about the image , which will be then used to embedded a watermarked key, directly in the intensity value of predefined regions of the image. Those pretty simple techniques provide a simple and effective way of embedding watermark in to the original image but don’t show robustness to common image alterations.
In the transform domain:-
Another way to produce a high quality watermark image , is by first transforming the original image into the frequency domain by the use of Fourier, Discrete Cosine or Wavelet transforms for example. With this technique, the marks are not added to the intensities of the image but to the value of its transform coefficients. Then, inverse-transforming the marked coefficients from the watermarked image. The use of frequency based transforms allow the direct understanding of the content of the image, therefore, characteristics of the human visual system (HVS) can be taken in to account more easily when it is time to decide the intensity and position of the watermarks to be applied to a given image.
Applications and Requirements of Invisible Watermarks
As previously stated, watermarking can be really useful in several areas of interest involving digital images. To fully understand the main challenges involved in the development of watermarking related tools, some applications of invisible watermarks are listed here to
Certification:
Digital watermarking allows to mutually link information on the documents. That means that some information is written twice on the document: for instance, the name of a passport owner is normally printed in clear text and is also hidden as an invisible watermark in the photo of the owner. If anyone would intend to counterfeit the passport by replacing the photo, it would be possible to detect the change by scanning the passport and verifying the name hidden in the photo does not match any more the name printed on the passport.
Copyright Protection ,owner Identification and Copy Protection :
For example conditional access to confidential data on CD-ROMs may be provided using digital watermarking technology. The concept consists of inserting a watermark into the CD label. In order to read and decrypt the data stored on the CD, the watermark has to be read since it contains information needed for decryption. If someone copies the CD, he will not be able to read the data in clear-text since he does not have the required watermark. The picture below shows an example of a protected CD. To read the data on the CD, the user starts a program on the CD. This program asks the user to put the CD on the scanner and then reads the watermark. If the watermark is valid the program decrypts the data on the CD and gives the user access the clear-text data.
"Still working on this"
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