Modeling the print-scan process for resilient data hiding

Print-scan resilient data hiding finds important applications in document security, and image copyright protection. In this paper, we build upon our previous work on print-scan resilient data hiding with the goal of providing a simple mathematical characterization for guiding the design of more sophisticated methods allowing higher volume of embedded data, or achieving more robustness. A model for print-scan process is proposed, which has three main components: a) effects due to mild cropping, b) colored high-frequency noise, and c) non-linear effects. It can be shown that cropping introduces unknown phase shift in the image spectrum. A new hiding method called Differential Quantization Index Modulation (DQIM) is proposed in which, information is hidden in the phase spectrum of images by quantizing the difference in phase of adjacent frequency locations. The unknown phase shift would get cancelled when the difference is taken. Using the proposed DQIM hiding in phase, we are able to survive the print-scan process with several hundred information bits hidden into the images.