1. An image processing method comprising the steps of: (a) obtaining a plurality of images of a subject each having a different resolution, and learning a resolution conversion rule from the plurality of images for each of subject characteristics; (b) obtaining an original image and dividing the original image into regions based on the subject characteristics; and (c) converting a resolution of the original image by applying to each of the regions obtained in step (b) the resolution conversion rule learned in step (a) regarding the subject characteristic corresponding to the region.