Watermarking for JPEG image authentication surviving integer rounding in decompression

A watermarking scheme for JPEG image authentication is proposed. It is a direct extension of Wong´s algorithm to JPEG-coded images where the signature is embedded at the end of scanned DCT coefficients. instead of LSB´s of raw pixel values. We address a problem that the watermark disappears after the integer rounding in JPEG decompression and show that imposing a restriction on the quantization step sizes for DCT coefficients can solve this problem. To avoid the limitation on compressed picture quality set by this restriction, we introduce an embedding technique to use different quantization vectors for the watermarking and the JPEG compression. Simulation results are shown to verify the proposed scheme.