A system for measuring temperature of one or more subjects within a scene including a reference object having an unknown emissivity, having an ambient temperature, the system comprising: a visible spectrum camera capable of acquiring images of the scene comprising (a) at least a Region of Interest (RoI) of each of the subjects, and (b) the reference object; a thermal image sensor capable of acquiring images of the scene comprising (a) at least the RoI of each of the subjects, and (b) the reference object; and a processing circuitry configured to: obtain (a) a visible spectrum image captured by the visible spectrum camera, and (b) a thermal image captured by the thermal image sensor, and (c) an indication of a scene ambient temperature within the scene; register the visible spectrum image and the thermal image onto a common coordinate system; identify (a) RoI pixels, on the common coordinate system, of the RoIs of the subjects within the visible spectrum image, (b) reference object pixels, on the common coordinate system, of the reference object within the visible spectrum image and (c) a parameter correlated to an emissivity of the reference object, based on the reference temperature and on the indication of the scene ambient temperature; determine (a) RoI temperatures by analyzing respective RoIs pixels on the thermal image, and (b) a reference temperature by analyzing the reference object pixels on the thermal image; and upon existence of a difference between the reference temperature and the scene ambient temperature, correct the RoI temperatures, based on the difference and utilizing the parameter, to compensate for the difference, giving rise to corrected RoI temperatures.