A personal authentication method is provided for authenticating a user by cross-relation between an enrolled image and a verification image of biometric information of the user. Upon registration of the biometric information, the method generates a filter for scrambling the image and an inverse filter thereof, and applies the filter to the enrolled image generated from the biometric information to generate a registration template which is then stored to a memory. Upon authentication of the user, the method applies the inverse filter to the verification image generated from the biometric information collected from the user, and then verifies the identity of the user based on cross-relation between the verification image after application of the inverse filter and the registration template.