A new approach of digital watermark based on information optics is presented. The watermark information is hidden in a halftone encoded computer-generated hologram. The watermark is encoded as a phase function of wave front by means of phase retrieval technique while the host information is taken as the amplitude of wavefront. Furthermore, the encoded wavefront is recorded through the computer generated hologram, and followed by a halftone encoding to achieve the watermark embedding process. The watermark can be retrieved by using either optical or digital Fourier transform on halftone images containing the watermarked information. The simulation results are presented and show good agreement with theoretical analysis. It is shown that the proposed watermarking technique is robust to various image processing operations. The binary characteristic of halftone encoded image grants the embedded watermark the ability to resist printing, hardcopy and scanning.