Data hiding and watermarking in JPEG-compressed domain by DC coefficient modification

JPEG is a common image format in the WWW and can potentially be used to hide data for secure internet communication and watermark for copyright control. In this paper, we propose an algorithm to embed the secret or watermark information. The proposed algorithm, named Watermarking by DC Coefficients Modification (WDCM), assumes that the quality factor used in JPEG compression is known. We observe that it is perceptually undetectable if the DC coefficients in certain texture-rich blocks are modified by a small amount. We thus embed the secret information as a binary bit sequence in the quantized DC coefficients in those texture rich blocks. The watermark embedding process can be applied in compression domain without re-encode the data. The information bits are randomized by some pseudo-random noise (PN) sequences, the keys of which are needed for the decoding of the secret information. By embedding the information in the DC components, the proposed algorithm is robust to common JPEG compression if the quality factor is known.