1. An image calibration method, comprising the steps of: receiving, at an image calibration processing device, a calibration request from a user terminal; receiving, at the image calibration processing device, a calibration object image photographed in accordance with an instruction for calibration photographing; performing a calibration process using the received calibration object image; receiving, at the image calibration processing device, a subject image transmitted from the user terminal and photographed by a camera used to photograph the calibration object image; performing a calibration on the subject image in accordance with results of the calibration process to form a corrected subject image; and returning the formed corrected subject image from the image calibration processing device to the user terminal.