A portable electronic device is disclosed. The portable electronic device includes: an image capturing device, for capturing a first image; a focal distance measuring device, for measuring a plurality of focal distances corresponding to a plurality positions of the first image; a display device, for outputting a picture; and a motion detecting controller, for determining variations of the plurality of focal distances measured by the focal distance measuring device when the portable electronic device moves or rotates, and controlling the picture shown in the display device according to the variations of the plurality of focal distances.