Blind digital watermarking technique using Fresnel hologram and phase encryption mask

In this paper, we present a new blind digital watermarking algorithm based on optical Fresnel hologram, phase encryption mask (PEM) and discrete wavelet transform (DWT). The watermark image is converted into Fresnel hologram by using phase encryption mask, and then it is embedded within the coefficient matrixes of the host image DWT. By using the pixel substitution in the coefficient matrixes, the original host image is no longer necessary in the process of withdrawing watermark information, and then the blind watermarking is obtained. Numerical experiments show that the algorithm is robust to the attacks, such as the JPEG lossy compressing, cropping, superposing noise and resampling from the screen copy. Because the encryption keys (phase encryption mask, diffraction distance and wavelength) can be designed in a large degree of freedom, the blind digital watermarking algorithm has high security and practical value.