Watermarking by encrypted Fourier holography
Sun Liujie · Optical Engineering · 2007
We propose and demonstrate a new encrypted Fourier holographic watermarking scheme based on double random phase encoding, digital holography, digital watermarking, and printing techniques. A digital watermark image to be hidden is encrypted by double random phase encoding with uniformly distributed random phase in both the input and Fourier planes. Using interference with a reference wave, an encrypted Fourier hologram is recorded digitally. The encrypted Fourier hologram can be hidden in a host image to protect the copyright. The watermark can be recovered by holographic reconstruction without the information of the host image (blind detection). Theoretical analysis and computer simulations prove that the new technique is valid and secure. The experimental results on the printing and scanning processes are presented to demonstrate that the proposed watermarked image can be used to prevent forgery of printed products.