Besides standard thermometers there are also thermometer cameras on the market. Thermometers measure the temperature only at one point or, in case it’s a noncontact thermometers (IR thermometer), of the viewed area (aperture angle of sensor). With these tools you detect hot areas but there not useful to find the real source of heat (average measuring in an area). With infrared cameras you get a thermal picture of the viewed area and detect in detail the hotspot and the source of heat. Depending on the used camera and the quality of the camera you can also measure the temperature.
The first picture shows different sensors mounted on the devices. With this method it is possible to get precise values of the temperature at the point of measurement. The normal measurement, with the glued sensors does not observe the temperature hotspots of the resistor and diode (second picture left bottom corner). Through IR-camera it’s easier to detect hotspots as shown in the next figure which gives a better overview.