Invertible Image Watermarking Based on Zero Coefficient Index

Invertible watermarking is a type of schemes which has the capability that recovers the host media without any loss after embedded data is extracted, and plays key roles in scenarios where exact host media are crucial. In practical applications, compressed images are widely used for easy storage and transfer. Proposed in this paper is a novel invertible watermarking method with high capacity and low distortion for compressed images, in which original compressed images can be exactly retrieved on the extracting side. A sequence of coefficients in the medium and high frequencies of a quantized DCT block is defined as the candidate position for embedding. As long as the maximum index of zero coefficients in this sequence is not smaller than the integer value of watermark bits, the proposed method can embed these bits by modifying only one zero coefficient. Since the ratio between the number of modified coefficients and the number of watermark bits is low, a large amount of watermark can be embedded with low distortion. Experimental results demonstrate that the capacity and quality of watermarked images of the proposed scheme are better than those of the schemes as reported in other state-of-the-art literature. In addition, the proposed scheme is also well adaptable and configurable.