1. A medical imaging apparatus comprising: an X-ray emitter configured to emit first X-rays and second X-rays toward an object; an X-ray detector configured to detect the first X-rays and the second X-rays that have been emitted to obtain a first X-ray image and a second X-ray image, corresponding to a plurality of areas of the object; a processor, which is configured to obtain information about a first detector location for obtaining the first X-ray image and information about a second detector location, wherein the X-ray detector moves from the first detector location, for obtaining the second X-ray image, is configured to generate a first virtual ruler based on a first distance from a reference point to the first detector location and a second virtual ruler based on a second distance from the reference point to the second detector location, and is configured to obtain a composite image by combining the first X-ray image and the second X-ray image based on the first virtual ruler and the second virtual ruler; and a display configured to display the composite image on which the first virtual ruler and the second virtual ruler are displayed, wherein, when a user input for moving the first X-ray image of the composite image along a first direction is received, the processor moves the first X-ray image along the first direction without moving the first virtual ruler, and the display is configured to display the first virtual ruler and the second virtual ruler on the composite image by aligning the first virtual ruler and the second virtual ruler as a one-dimensional ruler in correspondence to the first image and the second image.