A method of detecting a reflection in a first thermal image captured by a thermal image sensor and, a second image is captured by a visible light sensor, near infrared sensor, or short-wave infrared sensor having a field of view which overlaps a field of view of the thermal image. A relationship between coordinates in the thermal image and the second image is determined. A first object is detected in a first position in the thermal image. A candidate image area in a second position in the second image is analysed to determine if anx 10 object equivalent to the first object is present, the second position corresponding to the first position according to the relationship between the coordinates in the thermal image and the second image. In response to a determination that there is no equivalent object in candidate image area, it is determined that first object is a reflection.