Abstract: The invention relates to a method and an arrangement (1) for determining a group of persons (100) to be considered staying in an observation region (50) by considering exception markings (60) for other persons (200), wherein the group of persons (100) to be considered is a group of the persons (100) staying in the observation region (50) excluding the other persons (200) who stay in the observation region (50) and carry one of the exception markings (60). Thereby, the exception markings (60) are graphic pattern with at least one characteristic length ratio. In the method, at least one image is recorded of the observation region (50), and in the at least one image, the persons (100, 200) staying in the observation region (50) and optical signatures of the exception markings (60) are detected, wherein the detected optical signatures are assigned to detected persons (200).