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, wherein the comparing the acquired plurality of X-ray images in order to generate the at least one difference image comprises irradiating, by an X-ray generator, the target object with X-rays at a first position in order to acquire first X-ray data of the target object, and irradiating, by the X-ray generator, the target object with X-rays at a second position which is different from the first position.