1. An apparatus for unfolding a depth image, the apparatus comprising: a processor to control one or more processor-executable units: an input unit to receive inputted multiple depth images with respect to a same scene, each of the multiple depth images being photographed based on different modulation frequencies of a fixed photographing device; a depth fold estimator to estimate a number of depth folds based on a distance between multiple three-dimensional (3D) points of multiple pixels indicating the same location of the scene in the multiple depth images; and an output unit to output the multiple depth images from which one or more depth folds have been removed based on the estimated number of depth folds, wherein each of the multiple depth images being photographed comprises a different maximum depth value as measured by the fixed photographing device.