基于文字复杂度的抗打印扫描文本水印算法

A Print Resilient Watermark Scheme Based on Character Complexity

机密信息通过打印文档泄露已成为重要安全问题.在文档打印过程中嵌入数字水印,通过扫描打印件提取水印,进而追踪泄密源,是上述问题的一种有效解决方式.研究发现,自然文档中的相邻文字高度并不相同,并且文字高度相对关系经打印扫描等处理后能得到保留.据此,提出一种强鲁棒文本水印算法,并根据文字复杂度自适应地调整水印强度,以保证视觉效果.实验结果表明,使用该算法,水印文档在经历打印—扫描、复印—扫描、拍照等多种攻击后,其中信息仍能被正确提取.

As a kind of information leaking carrier, printed documents are recently becoming a large se- curity risk. Tracing document with watermarks is an effective resolution to the problem. It is found out that the heights of neighboring characters from nature text are usually not the same, and most height rela- tionships between character pairs keep reserved after print-scan. According to it, this paper proposes a new robust watermark method by modifying character＇ s height. Besides, only those character pairs with similar complexity will be chosen to achieve better transparency. Experiments show that the watermark can be extracted from the texts distorted due to print-scan, print-copy, or print-photograph.