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, providing distance information; estimating a candidate head area from the movement area based on the distance information; and determining 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.