Robust and blind image watermarking in DCT domain using inter-block coefficient correlation

This study presents a robust and transparent watermarking method that exploits block-based discrete cosine transform (DCT) coefficient modification. The difference in the DCT coefficients of two blocks is calculated and modified based on the watermark bit to adjust this difference to a predefined range. The first coefficient in the upper left corner of the array basis function is known as the direct current (DC) coefficient, whereas the remainder includes the alternating current (AC) coefficients. The extent of the DCT coefficient modifications depends on the DC coefficient and median of the AC coefficients ordered by a zig-zag sequence. The robustness of the proposed method against various attacks was evaluated experimentally, and experimental results demonstrate that the proposed method possesses great robustness against various single and combined attacks.