By using an ultraviolet-curable nematic liquid crystal material, some designed patterns can be stored in the liquid crystal cells with areas polymerized under isotropic and nematic phases. We have proposed a security device that uses the random pattern of optical texture in each cell. In other words, the random patterns of schlieren in each cell can be used as identifiers. For security system using these devices, it is necessary to develop the computer-based system capable of comparing optical texture patterns. In this research, methods of extraction of written patterns were studied for security system.