1. A method of acquiring a phalange edge image, comprising: (a) selecting a region of interest from an X-ray image of a hand; (b) acquiring a soft tissue background gray level removed image by removing a soft tissue background gray level from the region of interest; and (c) extracting a phalange edge image from the soft tissue background gray level removed image, wherein the step (b) of removing the soft tissue background gray level comprises: (b1) extracting a finger edge image from the region of interest, the finger edge image including a soft tissue region and a phalange region; (b2) performing fitting to interpolate a gray level of the soft tissue region in the finger edge image into the phalange region; and (b3) subtracting a gray level of an image obtained by the fitting from a gray level of the finger edge image in order to acquire the soft tissue background gray level removed image.