Journal of Computer Applications (计算机应用) 2013/33:12 PP.3522-3526
The deficiency of evaluation scheme for the imperceptibility of Natural Language Watermarking (NLW) seriously restricts the development in this field. To resolve this problem, combining the characteristics of natural language and the knowledge of psycholinguistics and considering the difficulty for human to understand natural language, an imperceptibility perceptual model and an automatic evaluation scheme were proposed. The proposed scheme evaluated the imperceptibility from three aspects: syntax error, collocation error and semantic loss. Finally, four different watermarking schemes including the T-Lex watermarking system based on absolute synonym substitution, the relative synonymous substitution watermarking system, the watermarking system based on syntactic tree and the Chinese syntactic watermarking system were used to compare the results of the proposed automatic method and manual method whose confidence coefficient is 90%. The two methods get the same conclusion: the imperceptibility of NLW based on word is better than that of NLW based on sentence, and the automatic evaluation scheme is effective for the imperceptibility of NLW.