A network construction system comprising: a video image analysis mechanism; and an association mechanism connected to the video image analysis mechanism; and a processor connected to the video image analysis mechanism as well as to the association mechanism; wherein: the video image analysis mechanism is adapted to process raw video image data of a plurality of cameras to provide an output of a body detection, body tracking, face detection and face tracking process, the output at least comprising a person ID for each face detection result; and the association mechanism is adapted to provide an output of a face association process using a similarity value for face detection outputs provided by the video image analysis mechanism; characterized in that the processor is adapted to detect following events, that form the basis for the links in the network structure, by using temporal pattern discovery and a space constraint, the following events being defined by at least two occurrences of a first person ID detected in a camera view at a first time and having a trajectory defined by an entry point and an exit point in the camera view of the first person ID and a second person ID in a said camera view at a second time after the first time and having a trajectory defined by an entry point an exit point in the camera view of the second person ID, both person IDs not being detected at the same time in the field of said camera view, both person IDs having similar general directions in the field of said camera view wherein both person IDs have similar general directions if an angle between the trajectory of the first person ID and the trajectory of the second person ID is less than forty-five degrees, and the temporal pattern and the space constraint being repeated in different spatial locations. a video image analysis mechanism; and an association mechanism connected to the video image analysis mechanism; and a processor connected to the video image analysis mechanism as well as to the association mechanism; the video image analysis mechanism is adapted to process raw video image data of a plurality of cameras to provide an output of a body detection, body tracking, face detection and face tracking process, the output at least comprising a person ID for each face detection result; and the association mechanism is adapted to provide an output of a face association process using a similarity value for face detection outputs provided by the video image analysis mechanism; characterized in that the processor is adapted to detect following events, that form the basis for the links in the network structure, by using temporal pattern discovery and a space constraint, the following events being defined by at least two occurrences of a first person ID detected in a camera view at a first time and having a trajectory defined by an entry point and an exit point in the camera view of the first person ID and a second person ID in a said camera view at a second time after the first time and having a trajectory defined by an entry point an exit point in the camera view of the second person ID, both person IDs not being detected at the same time in the field of said camera view, both person IDs having similar general directions in the field of said camera view wherein both person IDs have similar general directions if an angle between the trajectory of the first person ID and the trajectory of the second person ID is less than forty-five degrees, and the temporal pattern and the space constraint being repeated in different spatial locations.