Digital watermarking by using orthogonal line screens

With the rapid growth of information technology, more and more sophisticated machines for image duplication have been created to enable image reproduction in an efficient and convenient way. However, it raises a serious threat on intellectual property rights. The purpose of this study is to compose watermarks with orthogonal lines in an effort to protect copyright and to ensure anti-counterfeiting protection. To design the orthogonal line screen watermarks, vertical and horizontal threshold matrix are processed by digital halftoning and the effect of encryption and decryption on the printout of the anticounterfeiting watermarks was evaluated. The results showed that conducting orthogonal lines to encrypt messages in documents can be successfully carried out. This technique is also applied to encrypt answers of the problem sets in text books.