A watermarking method for halftone images based on iterative halftoning method

Abstract

This paper proposes a new watermarking method to embed invisible data in halftone images. Halftone images are binary images appearing in printed matters such as books. The embedded data in halftone images can be used for copyright protection. The data hiding is integrated into halftoning operation. Watermark bits are hidden at pseudorandom locations within a halftone image during halftoning process. In order to minimize the distortions due to the inserted watermark, the proposed method tries to find the best neighborhood pattern using iterative binary search method. In order to cope with unintentional attacks such as cropping and distortions, the watermark is inserted periodically in halftone images. Experiments show that the proposed method can hide the relatively large amount of data within a halftone image without causing noticeable artifacts and the watermark is robust to crop and geometrical distortion.