1. A method of counting a number of persons in at least one image frame, the method comprising: detecting a movement area in a top-view distance image, of the at least one image frame captured by a camera, providing distance information; estimating, via a processor, a candidate head area from the movement area based on the distance information; and determining, via the processor, whether the candidate head area is an actual head of a person based on a similarity to a circle of the candidate head area and a spherical curvature of the candidate head area estimated from the distance information about the candidate head area, wherein the estimating the candidate head area comprises: extracting a reference pixel, which corresponds to a greatest height from a ground surface in the at least one image frame, from the movement area; setting an expanded area comprising the reference pixel, surrounding pixels having a same height as the reference pixel, and surrounding pixels whose change in height is constant or decreasing; and setting the candidate head area comprising the reference pixel and surrounding pixels with heights that differ from the height of the reference pixel within a threshold value.