Semi-Fragile Watermark Based on Adaptive Quantization for Image Content Authentication

A novel semi-fragile watermark scheme for image authentication is proposed in this paper. New scheme extracts the image content features from the low frequency domain to generate watermarks, inserts obtained feature into the image by modulating the wavelet domain, and the watermark generation and embedment are disposed in the image. To enhance the robustness and invisibility, the adaptive quantization is used, and quantization step is calculated according to the local image characteristics. The integrity authentication and tamper detection are implemented by comparing the extracted watermark and the extracted content feature. Experimental result shows that the proposed scheme is robust to common image processing (such as JPEG compression, noise-adding, filtering), but malicious changes of the image will result in alarms of the watermark detection. In addition, proposed scheme can detect the exact locations-the illegal modified blocks.