1. A method for controlling an X-ray imaging apparatus, the method comprising: detecting, by the apparatus, X-rays which have propagated through a target object at at least two different positions in order to acquire a plurality of X-ray images; comparing the acquired plurality of X-ray images in order to generate at least one difference image based on the acquired plurality of X-ray images; and determining a modified portion which corresponds to a difference between at least two of the plurality of X-ray images based on the generated at least one difference image; and detecting at least one tissue which constitutes the target object by using the determined modified portion.