Pyramid-structure-based reversible fragile watermarking

This paper presents a novel reversible fragile watermarking scheme based on a pyramidal structure. The similarities among the detail components of a pyramid-structure image are exploited to select appropriate embedding areas, and then the cryptographic watermarks are embedded into selected wavelet coefficients using a difference-expansion method. An adaptive embedding method is proposed to avoid needing extra space to store parts of the original image and the watermark location map. The cryptographic signatures are created using a watermark generation function that comprises a hashing function and a public-key encryption function. To resist counterfeiting attack, block relationships are created using toral automorphism to increase the security and implementation practicability. Experimental results show that the proposed reversible fragile watermarking scheme can successfully obtain the original image if the protected image is unaltered, and unauthorized manipulations can be correctly identified and localized even when protected images undergo a cropping attack.