An enclosure having: a base face that is opaque or translucent to human eyes viewing from outside of the enclosure and transparent to infrared radiation; and at least two flat, orthogonal mounting faces configured to be overlaid respectively on at least two surfaces of walls and ceiling of a room. A thermal imaging apparatus configured to image based on infrared radiation and mounted within the enclosure with a predetermined orientation relative to the base face to have a designed imaging direction with respect to the room when the enclosure is mounted in the room to have the at least two orthogonal mounting faces overlaid respectively on the at least two surfaces.