We propose a watermarking scheme for hardcopy pictures based on computer-generated holography. A hologram of the watermark is produced using a conjugate-symmetric extension technique, and its spectrum is inserted into the discrete cosine transform domain of the image. Adjusting the watermark placement in a data array, a trade-off between transparency and robustness is achieved. Anticropping and the interference-resisting capability of holograms make the watermark robust against manipulations commonly performed on digital images during postprocessing, including contrast enhancement, moderate smoothing and sharpening, and, in particular, geometric transformation. Most importantly, the proposed hologram-based watermarking can withstand the printing-scanning attack and, therefore, is useful in protecting copyright of digital photographs both as electronic and hardcopy versions.
© 2010 Optical Society of America
Original Manuscript: October 13, 2009
Revised Manuscript: January 10, 2010
Manuscript Accepted: January 22, 2010
Published: February 26, 2010
Shuozhong Wang, Sujuan Huang, Xinpeng Zhang, and Wei Wu, "Hologram-based watermarking capable of surviving print-scan process," Appl. Opt. 49, 1170-1178 (2010)