The paper proposes a watermarking-based image tamper detection algorithm in the discrete cosine transform (DCT) domain. The scheme is designed to be robust to high JPEG compression, but it is also able to resist other content-preserving image processing operations. The watermark used for authentication is obtained by xoring a pseudo-random binary sequence generated using a private key with a block-dependent image feature. This authentication code is embedded in selected low-frequency DCT coefficients, quantized using a modified JPEG quantization matrix, protecting the algorithm against high JPEG compression. Compared to other existing approaches, the scheme achieves very good image quality and is able to detect and locate malicious attacks with good precision.

Keywords: Multimedia security, Digital watermarking, Tamper detection, Image authentication, Discrete cosine transform (DCT)