Nowadays, the surveillance of important areas such as shopping malls, stations, airports and seaports, is becoming of great interest for security purposes. In the last few years, we have witnessed the installation of a large number of cameras that now are almost covering every place in the major cities. Unfortunately, the majority of such sensors belong to the so-called second generation of CCTV surveillance systems where human operators are required to interpret the events occurring in the scene. Only recently modern and autonomous surveillance systems have been proposed to address the security problems of such areas. Many systems have been proposed for a wide range of security purposes from traffic monitoring to human activity understanding. Video surveillance applications often imply paying attention to a wide area, so different kinds of cameras are generally used, for example, fixed cameras, omni-directional cameras and pan, tilt and zoom (PTZ) cameras.
