1. A fingerprint data registering method, comprising: blurring a fingerprint-shaped pseudo image and displaying the blurred pseudo image; extracting a fingerprint position of a fingerprint image acquired for authentication registration; determining a position in the pseudo image, which corresponds to the extracted fingerprint position; converting a part of the blurred pseudo image at the corresponding position to a clear partial pseudo-image having a higher resolution than that of the blurred pseudo image and displaying the clear partial pseudo-image; and registering the acquired fingerprint image as an authentication-purpose fingerprint image in association with said converting and displaying, wherein the fingerprint position of the acquired fingerprint image is one of an inside area including a fingerprint core and an outside area surrounding the inside area, wherein the outside area includes a plurality of partial outside areas distributed around the fingerprint core, and wherein said extracting includes: extracting a fingerprint ridge from the acquired fingerprint image; measuring a curvature of the extracted fingerprint ridge; determining presence or absence of the fingerprint core based on a direction histogram using the measured curvature; and determining whether the fingerprint position is a fingerprint position in the inside area or a fingerprint position in the outside area, based on a determination result in said determining presence or absence of the fingerprint core.