1. Introduction
In realistic surveillance scenarios, it is impossible for a single sensor to monitor all areas at once or to acquire interesting event at high resolution. Objects become occluded by trees and buildings or by other moving objects, and sensors themselves have limited fields of view. A promising solution to this problem is to use a network of PTZ (Pan-Tilt-Zoom) cameras. A PTZ camera can be conceived as a reconfigurable fixed camera. In facts, through the pan, tilt and zoom parameters, we can actually choose one from a family of fixed cameras. The zoom capabilities of those cameras allow to place them away from the scene to monitor, while the pan and tilt can be used to cooperatively track all objects, within an extended area, that could not be viewed by a single not zooming sensor.