A Review of Text Watermarking: Theory, Methods, and Applications <s> III. APPROACHES USED IN TEXT WATERMARKING <s> Summary form only given. Electronic documents are more easily copied and redistributed than paper documents. This is a major impediment to electronic publishing. Illegal redistribution can be discouraged by placing unique marks in each copy and registering the copy with the original recipient. If an illegal copy is discovered, the original recipient can be identified. We describe several invisible techniques for encoding information in text documents. We also describe a marking system, for electronic publishing, that is scalable to large numbers of users. <s> BIB001 </s> A Review of Text Watermarking: Theory, Methods, and Applications <s> III. APPROACHES USED IN TEXT WATERMARKING <s> Each copy of a text document can be made different in a nearly invisible way by repositioning or modifying the appearance of different elements of text, i.e., lines, words, or characters. A unique copy can be registered with its recipient, so that subsequent unauthorized copies that are retrieved can be traced back to the original owner. In this paper we describe and compare several mechanisms for marking documents and several other mechanisms for decoding the marks after documents have been subjected to common types of distortion. The marks are intended to protect documents of limited value that are owned by individuals who would rather possess a legal than an illegal copy if they can be distinguished. We will describe attacks that remove the marks and countermeasures to those attacks. An architecture is described for distributing a large number of copies without burdening the publisher with creating and transmitting the unique documents. The architecture also allows the publisher to determine the identity of a recipient who has illegally redistributed the document, without compromising the privacy of individuals who are not operating illegally. Two experimental systems are described. One was used to distribute an issue of the IEEE JOURNAL ON SELECTED AREAS IN COMMUNICATIONS, and the second was used to mark copies of company private memoranda. <s> BIB002 </s> A Review of Text Watermarking: Theory, Methods, and Applications <s> III. APPROACHES USED IN TEXT WATERMARKING <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> BIB003 </s> A Review of Text Watermarking: Theory, Methods, and Applications <s> III. APPROACHES USED IN TEXT WATERMARKING <s> The using of the internet with its technologies and applications have been increased rapidly. So, protecting the text from illegal use is too needed . Text watermarking is used for this purpose. Arabic text has many characteristics such existing of diacritics , kashida (extension character) and points above or under its letters .Each of Arabic letters can take different shapes with different Unicode. These characteristics are utilized in the watermarking process. In this paper, several methods are discussed in the area of Arabic text watermarking with its advantages and disadvantages .Comparison of these methods is done in term of capacity, robustness and Imperceptibility. <s> BIB004 </s> A Review of Text Watermarking: Theory, Methods, and Applications <s> III. APPROACHES USED IN TEXT WATERMARKING <s> Data protection from malicious attacks and misuse has become a crucial issue. Various types of data, including images, videos, audio and text documents, have given cause for the development of different methods for their protection. Cryptography, digital signatures and steganography are the most well known technologies used to protect data. During the last decade, digital watermarking technology has also been utilized as an alternative to prevent media forgery and tampering or falsification to ensure both copyright and authentication. Much work has been done to protect images, videos and audio but only a few algorithms have been considered for text document protection with digital watermarking. However, our survey observed that available text watermarking algorithms are neither robust nor imperceptible and as such remain unsecured methods of protection. Hence, research to improve the performance of text watermarking algorithms is required. This paper reviews current watermarking algorithms for text documents and categorizes text watermarking methods based on the way the text was treated during the watermarking process. It also discusses merits and demerits of available methods as well as recent proposed methods for evaluating text watermarking systems and the need for further research on digital text watermarking. <s> BIB005
Research on text watermarking began in 1997 where several text watermarking approaches were proposed for encoding information in text documents and copyright protection BIB001 . This initial research has prompted other researchers to give more serious attention to the study of text watermarking. These early proposed approaches of text watermarking included structural based watermarking, where the line, letters and spaces are shifted to embed the bits of the watermark BIB002 . Later, linguistic based watermarking approach was proposed  . For this method the language of the text is analyzed and edited to embed watermark bits. Since then a lot of other innovative approaches have been proposed and classified BIB003 - BIB004 , BIB005 . In this study, we examine and evaluate the structural-based, the linguistic-based, and the image-based approaches.