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Top1. Introduction
Digital image watermarking techniques seek to embed a hidden signal known as a watermark into an image. The confidential information can be in different types of digital media such as audio, video, text, and printed documents. Digital image watermarking has many applications, including intellectual property security, tracking, detecting tamper information in the property, correct document mark, evaluating the authenticity, fingerprinting, and channel protection at the receiver and sender. The secret information hidden behind digital media is known as watermark, which represent the aunticity of data. On the other hand, the digital media which is used to hide the information is known as carrier signal or carrier object.
However,when embedding the watermark, the watermarking process can add only a minimal amount of noise or distortions. Losses should be held to a minimum. The accessibility of digital data would be harmed if there are so many distortions. The majority of watermarking systems in use today are not lossless. Some most attractive features of the most recent watermarking system are: imperceptibility, robustness, capacity and computational complexity. The watermarked signal's robustness refers to its ability to withstand attacks or distortions caused by malicious data processing. This feature allows watermarked photos to be used legally. The next important feature imperceptibility says that the original signal and the marked signal must be indistinguishable. The third very essential requirement of watermark, capacity represent tthat the cover object size is sufficient to hide the secret information without violating its imperceptibility quality.The last but not the least fetures computational complexity says that the cost of embedding a watermark in a host image and removing the watermark from the watermarked image should be as low as possible.
The three major categories of digital watermarking techniques are focused on domain, document form (text, picture, music, or video), and human perception. Based on human perception the watermark can be brodly classified as visible and invisible watermark. As the name implies in the visible watermak, the watermark is clearly visible on carrier objects. Watermarking, on the other hand, is designed to be totally invisible. The watermark's actual bits must be dispersed across the file in such a way that they cannot be detected and tampered . As a result, the watermarking must be strong enough to withstand normal file changes, such as noise attacks.
The second categorization of watermark depend upon As discussed earlier based on the type document form of secret information and these are: trext watermak,image watermark, audio watermark and video watermark.
Depending upon the domain the watermarking technique is brodally classified as Spatial domain watermark and frequency (transform) domain technique.Both domains are distinct, each with its own set of advantages and disadvantages, and each is used in a particular scenario. The former one operate directly on the pixels of the original image. The watermark can be added by modifying pixel values based on the author's logo or signature detail. The main aim of frequency domain is to embed the watermarks in the image's spectral coefficients. The Discrete Cosine Transform (DCT), Discrete Fourier Transform (DFT), and Discrete Wavelet Transform (DWT) are the most widely used transforms. The explanation for watermarking in the frequency domain is that the spectral coefficients better capture the characteristics of the human visual system (HVS). Watermarking in the spatial domain is simpler and faster than in the transform domain, but it is less resistant to attacks. Any image can be processed using spatial domain techniques. The most important spatial domain approach is LSB.Watermarking in the spatial domain is simpler and faster than in the transform domain, but it is less resistant to attacks. Any image can be processed using spatial domain techniques. The most important spatial domain approach is LSB. This paper mainy survey on implemented digital watermark technique used by LSB approach.