Introductory Chapter: Digital Image and Video Watermarking and Steganography Introductory Chapter: Digital Image and Video Watermarking and Steganography

Watermarking and steganography are important cryptographic operations on images and videos. Watermarking embeds the ownership symbol in images and videos either visually or invisibly. Steganography hides small piece of information in images and videos invisibly. Watermarking is used mainly for copyright protection, whereas steganography is used to send secret messages. Table 1 presents the difference between watermarking and steganography.


Overview of watermarking and steganography
Watermarking and steganography are important cryptographic operations on images and videos. Watermarking embeds the ownership symbol in images and videos either visually or invisibly. Steganography hides small piece of information in images and videos invisibly. Watermarking is used mainly for copyright protection, whereas steganography is used to send secret messages.

Challenges in the development of watermarking algorithms
Quality of the watermarking techniques can be accessed through various metrics such as peak signal-to-noise ratio (PSNR), signal-to-noise ratio (SNR), structural similarity index measurement (SSIM), and normalized crosscorrelation (NCC). Most of the real-world application requires good imperceptibility and high robustness. Achieving both of them simultaneously for color images and multimedia documents sought highly efficient watermarking algorithms. Hence, obviously transform domain processing will be the natural choice to meet out these complex requirements.
Fourier transform, discrete cosine transform, radon transform, and wavelet transform are the commonly used transformations for embedding watermarks. Fourier transform provides good resistance against geometric attacks. Discrete cosine transform yields robustness when watermarked images are compressed. Wavelet transform archives good imperceptibility and radon transform can provide good robustness. Though each transform is advantages in its own way, only careful development of watermark embedding and extraction algorithms helps in achieving maximum advantage of the chosen transformation.

Challenges in the development of steganography algorithms
Steganography algorithms can be classified based on the type of data employed as (1) text steganography, (2) image steganography, (3) audio steganography, and (4) video steganography.

Conclusion
In this introductory chapter, applications and challenges of both watermarking and steganography are presented. Researchers continue to develop new and efficient watermarking and steganography algorithms. Since huge amount of data are getting digitized, establishing ownership and sharing them secretly are becoming a challenging task. In this book, five interesting algorithms, three for watermarking and two for steganography, are available.