1. A method of identifying an object which is within or passes through a designated area, the method comprising: acquiring first 3D image data representing the object while the object is within or passes through the designated area; determining second 3D image data representing the object's surface based on the first 3D image data; checking the quality of the second 3D image data; comparing the second 3D image data to data representing known objects; and identifying the object based on the second 3D image data.