1. An image connection method, comprising: using a computer to execute: continuously inputting fingerprint images by relative movement of a finger in same direction with respect to a read unit sequentially reading biometric portion images of the finger as the fingerprint images; extracting a first character shapes from two of the input fingerprint images; calculating, as a first evaluation value, a sum of products of overlapping pixels in duplicating areas of the two fingerprints, for each relative transfer position of the two first character shapes while relatively moving the two first character shapes; detecting an amount of movement of a transfer position of the two first character shapes having a maximum evaluation value from among the plurality of first evaluation values; extracting second character shapes from the two first character shapes when there is no significant maximum value from among the plurality of first evaluation values; calculating, as a second evaluation value, a sum of values obtained by multiplying, with a predetermined weight, the products of two overlapping pixels in duplicating areas of the two fingerprint images and adding the sum to the first evaluation value, for each relative transfer position of the two second character shapes while relatively moving the two second character shapes; detecting an amount of movement of a transfer position of the two second character shapes having a maximum evaluation value from among the plurality of second evaluation values; and connecting the two fingerprint images to each other as adjacent fingerprint images, based upon the detected amount of movement of the first and/or second character shapes having the maximum evaluation value to generate a fingerprint image larger than a sensing surface of sensor of the read unit.