ABSTRACT
This chapter describes the fundamentals of watermark-based image authentication. It presents the main motivations and the rationale for research, development, and use of this technology. The chapter provides a brief review of state-of-the-art techniques for image authentication. It analyzes theoretical and practical aspects related to feasibility, effectiveness, and security. The chapter also describes a technique for fragile image authentication derived from the extreme sensitivity of linear ill-posed operators to small distortions in the input data. Semifragile watermarking addresses content verification, assuming that some image changes are allowed before, during, or after transmission and the transformed image is still regarded as genuine. Fragile watermarking treats any manipulation of the original image as unacceptable and addresses authentication with well-defined tamper-detection properties. In most cases, cropping of watermarked images leads to severe desynchronization between the boundaries of the block used in the watermarking process and those used in the verification.
