1. A method to detect and count people using a depth camera, the method comprising: receiving an image captured by the depth camera; converting the image, in a depth camera coordinate system, to an image in a real space coordinate system based on an angle and a position of the depth camera relative to at least one subject of the image; detecting at least one subject from the image in the real space coordinate system; calculating a distance from the depth camera to the at least one subject based on the image in the real space coordinate system; and determining whether the at least one subject is a person using criteria that varies depending on a respective calculated distance from the depth camera to the at least one subject, wherein the criteria includes a first similarity of the at least one subject with respect to a first shape and a second similarity of the at least one subject with respect to a second shape, and wherein the determining includes: if the calculated distance is within a predetermined threshold distance, comparing the at least one subject to the first shape; and if the calculated distance is beyond the predetermined threshold distance, comparing the at least one subject to the second shape.