More secure lossless visible watermarking by DCT

This study proposes a scheme for using modified coefficients of the DCT of an image to generate a lossless visible watermark. The major contribution of the proposed technique is the improved security against attack to remove watermarks under stricter assumption of Kerckhoffs’ principle. After the host images and watermarks are decomposed into several frequencies, the DCT coefficients of the watermark are embedded into the DCT coefficients of the host image. Integer mapping is then used to perform 2-dimensional DCT. The major advantage of the method is the improved security achieved by using a random permutation matrix to factorize the transformation matrix. That is, since the embedding stage multiplies the transformation matrix by a random permutation matrix, illicit users, even under the stricter assumption of Kerckhoffs principle that the proposed embedding method is known by illicit users, cannot properly recover the host image without the correct permutation matrix. Unlike methods that embed the watermark in quantized frequency-domain coefficients, the watermarked image remains in raw lossless image form instead of some lossy form of quantized coefficients e.g., JPEG-formatted. Maintaining the lossless format of the watermarked image provides reversibility.