Digital Watermarking: A Tutorial

—Due to high speed computer networks, the use of digitally formatted data has increased many folds. The digital data can be duplicated and edited with great ease which has led to a need for effective copyright protection tools. The process of embedding additional data along with the digital audio, images and video is called digital watermarking. A number of watermarking techniques have been proposed in literature. This paper is a tutorial in general watermarking principles and focuses on describing various watermarking techniques. I. INTRODUCTION In recent times, due to great developments in computer and internet technology, multimedia data i.e. audio, images and video have found wide applications. Digital watermarking is one of the best solutions to prevent illegal copying, modifying and redistributing multimedia data. Encryption of multimedia products prevents an intruder from accessing the contents without a proper decryption key. But once the data is decrypted, it can be duplicated and distributed illegally. To enforce IP rights and to prevent illegal duplication, interpolation and distribution of multimedia data, Digital watermarking is an effective solution. Copyright protection, data authentication, covert communication and content identification can be achieved by Digital watermarking. Digital watermarking is a technique to embed copyright or other information into the underlying data. The embedded data should maintain the quality of the host signal. In order to achieve the copyright protection, the algorithm should meet few basic requirements i) Imperceptibility: The watermark should not affect the quality of the original signal, thus it should be invisible/ inaudible to human eyes/ ears. ii) Robustness: The watermarked data should not be removed or eliminated by unauthorized distributors, thus it should be robust to resist common signal processing manipulations such as filtering, compression, filtering with compression. iii) Capacity: the number of bits that can be embedded in one second of the host signal. iv) Security: The watermark should only be detected by authorized person. v) Watermark detection should be done without referencing the original signals. vi) The watermark should be undetectable without prior knowledge of the embedded watermark sequence.