A method of authenticating users is provided that includes capturing biometric authentication data of a user and processing the captured biometric data into an image. Moreover, the method includes determining a region of interest of the image and a gray scale image from the image, determining an optimum transformation parameter set within the region of interest, and aligning the gray scale image with an enrollment gray scale image generated during enrollment of the user using results of the optimum transformation parameter set determination. Furthermore, the method includes extracting biometric feature data from the gray scale image and verifying an identity of the user with extracted biometric feature data included in a region of agreement.