What is a thermal imager used for?

Generally used to do equipment troubleshooting, to find abnormal heat in the high-temperature zone, or low-temperature zone, and now also used for large-scale portraits of temperature measurement (for the epidemic), which is more common in the civilian field (observation of wildlife, filming documentaries, etc., will also be used, but uncommon; the rest of the military field, the dark environment can be scanned inside the living body, and can even add the enemy to identify markers.