Research On Digital Watermark Available For Printed Images

In this paper, digital watermarking available for printed images is researched. It is concrete to study the contents as follows:1. The distortion introduced by print/scan process to images is discussed. According to the result, robustness of already proposed algorithms is analysised.2. An algorithm resistant to print/scan process is proposed, which is based on block discrete Fourier transform. New algorithm is more robust than already proposed algorithms.3. An algorithm based on fractional Fourier transform (FFT) is proposed, which is available for printed images. The FFT order is required as a key in detection. And its changeability makes the encrypted images more difficult to be counterfeited.4. An overview of already proposed watermarking algorithms for halftone images is given. Four algorithms among them are compared with each other. The result of comparison demonstrates that different algorithm has different advantage and disadvantage, which algorithm to be adopted can be decided according to practice demand.