Abstract
The widespread use of Internet and other communication technologies has brought about ease in reproducing, disclosing and distributing digital content. In addition to getting the benefits of information exchange, the digital community is confronted with authentication, forgery and copyright protection issues. Text is the most frequently used medium travelling over the Internet, along with images, audio and video. Majority of the content of books, newspapers, web pages, advertisements, research papers, legal documents and many other documents is basically, plain text. Therefore, copyright protection of plain text is a most important issue. In this article, we propose a robust zero-watermarking algorithm based on prepositions and double letters for copyright protection of plain text. The embedding algorithm uses occurrences of prepositions and double letters in the text to generate a key based on watermark. The extraction algorithm extracts the watermark from the noisy text to identify the original owner. Experimental results illustrate the effectiveness of the proposed algorithm on text encountering combined insertion, deletion and re-ordering attacks, both in the dispersed and localized forms. The results are also compared to a recent work on text watermarking.