You thought images that you pick up are all yours? Think again, they may be secure enough with a Watermark that could be very well traced down.
A digital Watermark is a digital signal or pattern inserted into a digital image. Since this signal or pattern is present in each unaltered copy of the original image, the digital Watermark may also serve as a digital signature for the copies. The desirable characteristics of a Watermark are
• Watermark should be resilient to standard manipulations of any nature.
• It should be statistically irremovable
Every Watermarking system consists at least two different parts:
• Watermark Embedding Unit
• Watermark Detection and Extraction Unit
In this paper, we discuss an algorithm for embedding and detecting the Watermark in a still image. A robust, secure, invisible Watermark is imprinted on the image I, and the Watermarked image WI, is distributed. The author keeps the original image I. To prove that an image WI' or a portion of it has been pirated, the author shows that W' contains his Watermark (to this purpose, he could but does not have to use his original image I). The best a pirate can do is to try to remove the original W Watermark (which is impossible if the Watermark is secure).
There can be another way out for the pirate, as to embed his signature in the image. But this does not help him too much because both his "original" and his Watermarked Image will contain the author's Watermark (due to robustness property), while the author can present an image without pirate's Watermark. Thus, the ownership of the image can be resolved in the court of law.
We have done the implementation in MATLAB and doing the simulation in C++..
Watermark, Transform Domain, DCT, FFT, Picture Cropping.
The enormous popularity of the World Wide Web in the early 1990's demonstrated the commercial potential of offering multimedia resources through the digital networks. Since commercial interests seek to use the digital networks to offer digital media for profit, they have a strong interest in protecting their ownership rights. Digital Watermarking has been proposed as one way to accomplish this.
A digital Watermark is a digital signal or pattern inserted into a digital image. Since this signal or pattern is present in each unaltered copy of the original image, the digital Watermark may also serve as a digital signature for the copies.
A given Watermark may be
• Unique to each copy (e.g., to identify the intended recipient), or
• Be common to multiple copies (e.g., to identify the document source)
In either case, the Watermarking of the document involves the transformation of the original into another form. This distinguishes Digital Watermarking from Digital Fingerprinting, where the original file remains intact, but another file is created that “best describes" the original file's content. As a simple example, the Checksum field for a disk sector would be a fingerprint of the preceding block of data. Similarly, Hash Algorithms produce fingerprint files.
Digital Watermarking is also to be contrasted with Public-Key Encryption, which also transforms original files to another form. It is a common practice nowadays to encrypt digital documents so that they become un-viewable without the decryption key. Unlike encryption, however, Digital Watermarking leaves the original image or basically intact and recognizable. In addition, Digital Watermarks, as signatures, may not be validated without special software. Further, decrypted documents are free of any residual effects of encryption, whereas Digital Watermarks are designed to be persistent in viewing, printing, or subsequent re-transmission or dissemination.
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