JPEG Images Authentication with Discrimination of Tampers on the Image Content or Watermark

The existing compressed-domain fragile watermarking scheme cannot effectively discriminate tampers on the image contents or the embedded watermark or both tampered by attackers; hence, a novel compressed-domain fragile watermarking scheme with the discrimination of tampers on the image content or watermark based on a chaotic system is proposed in this paper. The quantized discrete cosine transform (DCT) coefficients of seven most significant bits (MSBs) after decoding are mapped to the initial values of the chaotic system, and then a content-based fragile watermark is generated by chaotic motion. After watermark permutation by the chaotic sequence, the operations of embedding and extracting the improved security watermark are all in the compressed domain. During authentication, the proposed method is able to detect the tampered location and discriminates tampers on the image content or watermark from the distribution density of nonzero elements in the tamper detection matrix. The quantized DCT coefficients after decoding are used directly for watermark embedding, which avoids the quantization effect on the detection of watermarks. Therefore, the proposed algorithm is very suitable for the JPEG image authentication. Furthermore, thanks to the high sensitivity to initial values and the good randomness of the chaotic system, the very accurate localization is not only realized for the malicious tampers to JPEG images, but also indicates whether the modification made to the watermarked image is on the image contents or the embedded watermark or both. Simulation results show the abilities of tamper discrimination and tamper localization of this technique.