Print-Scan Resilient Text Image Watermarking Based on Stroke Direction Modulation for Chinese Document Authentication

Abstract

Abstract. Print-scan resilient watermarking has emerged as an attractive way for document security. This paper proposes a stroke direction modulation technique for watermarking in Chinese text images. The watermark pro-duced by the idea offers robustness to print-photocopy-scan, yet provides relatively high embedding capacity without losing the transparency. During the embedding phase, the angles of rotatable strokes are quantized to embed the bits. This requires several stages of preprocess-ing, including stroke generation, junction searching, ro-tatable stroke decision and character partition. Moreover, shuffling is applied to equalize the uneven embedding capacity. For the data detection, denoising and deskewing mechanisms are used to compensate for the distortions induced by hardcopy. Experimental results show that our technique attains high detection accuracy against distor-tions resulting from print-scan operations, good quality photocopies and benign attacks in accord with the future goal of soft authentication.