A Review of Text Watermarking: Theory, Methods, and Applications <s> B. IMPERCEPTIBILITY <s> Copyright protection of plain text while traveling over the internet is very crucial. Digital watermarking provides the complete copyright protection solution for this problem. Text being the most dominant medium travelling over the internet needs absolute protection. Text watermarking techniques have been developed in past to protect the text from illegal copying, redistribution and to prevent copyright violations. This paper presents a review of some of the recent research in watermarking techniques for plain text documents. The reviewed approaches are classified into three categories, the image based approach, the syntactic approach and the semantic approach. This paper discusses the main contributions, advantages and drawbacks of different methods used for text watermarking in past. <s> BIB001 </s> A Review of Text Watermarking: Theory, Methods, and Applications <s> B. IMPERCEPTIBILITY <s> Copyright protection of digital contents is very necessary in today’s digital world with efficient communication mediums as internet. Text is the dominant part of the internet contents and there are very limited techniques available for text protection. This paper presents a novel algorithm for protection of plain text, which embeds the logo image of the copyright owner in the text and this logo can be extracted from the text later to prove ownership. The algorithm is robust against content-preserving modifications and at the same time, is capable of detecting malicious tampering. Experimental results demonstrate the effectiveness of the algorithm against tampering attacks by calculating normalized hamming distances. The results are also compared with a recent work in this domain <s> BIB002
Imperceptibility is the ability of the watermark to remain unnoticed by the naked eye. This is achieved by the high level of similarity between the original data and the watermarked data. The original data should be almost the same after the data are hidden and should not degrade its content. It aims at adding invisible data hidden in the text, preserve its integrity and as copyright protection. Although it is common that watermarked data is imperceptible, digital watermark embedded can be visible or invisible BIB001 , BIB002 . In visible watermarking, the embedded watermark is obvious and can be detected by the naked eye. This is usually done in images and videos in order to prevent their unauthorized distribution. The watermark signals clearly that the document is owned and that any form of tempering and copying is not permissible. Text content can be easily manipulated and copied, and therefore, the invisibility of the watermark data is important. The invisible watermark is embedded in the document in such a way that it cannot be seen by the naked eye. It can, however, be detected by algorithm. The mathematical expressions as shown below signify that imperceptibility can be formulated in such a way that the watermarked data are approximately the same after being tampered with.