The equipment measures minute changes in temperature at the skin surface and reports this information as a color-encoded photograph. Underlying soft tissue and bony injuries raise the temperature of the surrounding tissues. These increases in temperature are often readily detectable by direct palpation, however changes in temperature of less than 2 degrees are not detectable to human touch.
Thermography can detect temperature differences of less than one-half of a degree.
Your event horse has just not been right. He seems to be getting a bit stiff to the right, and he's been grouchy when you are grooming him and getting him tacked up. No definite lameness. But something isn't right, you tell your veterinarian. You haven't given your practitioner much to go on, and he isn't seeing much when you walk and jog the horse.