Despite what you might have seen on television or in movies, thermographic imaging cameras can't see behind walls. Instead, they detect temperature variations related to heat and moisture along building surfaces.
Anything with a temperature above absolute zero emits heat. A thermal camera is able to detect this heat and create a thermal image based on that information. A qualified professional then examines the thermal image and assesses what's potentially going on behind the surface that's causing the temperature variations in the thermal image.
Thermographic imaging cameras can detect serious problems the naked eye can't see, such as:
The only way to detect insulation problems without tearing down your walls is by using a thermographic imaging camera.
A qualified inspector can detect if there is adequate insulation in your walls and attic space by using a thermal camera. During warmer months of the year the inspector is looking for warm spots in the thermal image whereas in the winter they're looking for cool spots.
The image on the right is a picture of a ceiling inside a home. Everything seems to fine. But a thermal image reveals heat penetration due to insufficient insulation.
Because the thermal image was taken in the summer the interior surface should be cooler than outside. This is indicated by the darker purple areas. But the yellow/orange area at the apex of the ceiling indicates that heat is penetrating through, which tells a qualified inspector there's a problem with the insulation in that area.