Text Image Authentication Techniques

In the late 20th century, security issues on digital multimedia become a hot research in the information security field. As a special kind of digital media, text image plays a decisive role in social life. In the current fragile internet security mechanism, there are lots of security problems in using some important text images. Therefore, it is necessary to study text image authentication in-depth in order to protect these important texts.Firstly, the current research status about text image authentication is introduced and analyzed in the first two chapters of this paper. Then binary text images authentication and robust image authentication is studied in-depth respectively in the last three chapters. The main results to the research are as follows:(1) Because current binary text image authentication algorithm cannot effectively solve the problem that tampering authentication to the uniformity of image, a new binary text image authentication algorithm based on short digital signature is proposed. In this new algorithm, the distribution of the uniform area in the image is extracted to a short signature, which can effectively solve the issue tampering authentication to the uniformity of image. With good invisibility, the algorithm has the theoretical probability of tamper detection 75% to the non-uniform area of the image.(2) Through observing and analyzing, it is found that turning the centre pixel of The-16-Blocks does not change the number of runs to the row or column scan vectors of the binary text image. Based on this feature, a new binary text image authentication algorithm based on watermark is designed, by which the uniform area of the image can be certified and high accuracy positioning can be achieved. The experiments show that the algorithm can effectively certificate the uniform areas of the image, with a higher tampering detection rate and good invisibility.(3) Considering the characteristics of the character structure, a new text image feature extracting method is designed. Experimental results show that this image feature extracting method has a certain anti-noise ability and it can be used for text image content authenticating and tamper locating. (4) A wavelet domain watermark embedding method is improved. The poor invisibility of the original algorithm is highly improved by reducing the number of parameters to modify. Experimental results show that the robustness of the improved embedding method is slightly worse than the original one, but the invisibility is much better than the original one. The improved algorithm can be used for protecting the copyright and authenticating the content of the text image.(5) The necessity of authenticating the content of the gray text image is proposed in the paper. Combing with the conclusions of (3) and (4), a robust text image content authentication algorithm is proposed. Experiments show that the algorithm has a tampering detecting probability 50% to the gray text image, and the invisibility and robustness works well.