**8. Conclusion**

We have studied optical security systems for practical applications in verification of the authenticity, such as in a card system. The advantages of the optical method in a security are the fast decoding of an encrypted image and the identification of it. Firstly, we study a common method of joint transform correlation for optical security systems and the optimization of binary holograms and proved that the optimization of a hologram will be a powerful tool in the systems. As an alternative method, a phase-coding technique is introduced to congenital with the uses of real optical devices in optical security systems. Originally, the merit of optical systems is fast processing of decryption of hologram and identification of it. However, the methods discussed here, i.e., not only image encryption, but also decryption of hologram and identification of it, can be applicable in all-digital techniques using a recent fast computer.
