Robust and blind watermarking technique in DCT domain using inter-block coefficient differencing

In this paper, a robust blind watermarking technique, based on block-based DCT coefficient modification is proposed. The difference between two DCT coefficients of the adjacent blocks at the same position is calculated. Depending upon the watermark bit to be embedded; this difference is brought in a particular predefined range which is achieved by modifying one of the two DCT coefficients. The amount of modification to a DCT coefficient of a block depends upon the scaling variable, DC coefficient and median of certain zig-zag ordered AC coefficients of that block. The robustness of the proposed scheme has been examined for various singular and hybrid attacks. Comparison results reveal that the proposed technique has a higher degree of robustness against various singular and hybrid attacks. Further a watermark of good quality is extracted even after various simultaneous attacks on the system.