A monitoring system for generating a three-dimensional (3D) image, the system including: a plurality of monitoring cameras which are arranged to capture respective images of an area such that a portion of an angle of view of one monitoring camera overlaps a portion of an angle of view of another monitoring camera; and a controller which crops a plurality of overlapped images, each of which is an image of the overlapped portion, from among the respective images captured by the plurality of monitoring cameras, and generates a 3D image by adding the overlapped images.