No magic here, just a difference in temperature.  Thermal imaging cameras take a picture in the infrared light band which is not visible to the naked eye.  These cameras can detect the difference in radiation that a warmer object emits vs a colder object.  The hotter an object is the more radiation it puts out.  Thermal imaging cameras can detect this temperature difference (or delta T) very accurately, usually to within .1 degrees.  They then convert those temperature differences to a color code and produce a picture.  It is sensitive enough to see the difference in temperature transferred from a handprint or a glass of water.

We use the FLIR E4 thermal camera.  This technology becomes very useful for safety issues in the main electrical panel with breakers that are close to failing or are loose and arcing as in the first two examples.  It helps to point out air lock in a radiator or prove that a well pressure tank bladder is intact and the tank is not water logged.  It can verify in-floor heating is operating or insulation damage under siding that is causing heat loss and frost forming on the interior walls.  No magic here, just a difference in temperature.  All included with our inspections!