A system for distinguishing a first group of persons from a second group of persons among plural persons who are present inside an area, and the system includes processing circuitry that: detects first positions of the plural persons who are present inside the area based on a heat image; detects second positions of the second group of persons who are present inside the area based on identification signals transmitted from portable wireless terminals of the second group of persons; and determines, as the first group of persons, those who are present at positions different from the second positions based on the first and second positions.