Abstract: The invention relates to an automatic surveillance system whereby characteristic data are first determined from a section of a signal (an instantaneous video image) using an automatic image analysis. This data is then stored temporarily or permanently with a time tag, so that it can be compared statistically with certain other time references. This statistical comparison enables the inventive surveillance system to identify abnormal situations and to selectively bring them to the attention of the surveillance officer. The invention is characterized in that the system itself identifies which situations are abnormal and require closer examination. It is not necessary to specify in advance what constitutes abnormal in a given surveillance situation, since after a certain period of running, the system itself will have collected the data corresponding to a normal situation.