You've probably seen the effects and results of infrared cameras in various Hollywood movies. They may seem like space age high tech devices, but they are also used by many photographers here on earth. Infrared cameras are able to produce an image by using infrared radiation, the way a regular camera can produce an image using visible light.
Everything produces black body radiation as a function of its temperatures. Typically, things that are hot produce more infrared radiation than cold objects. The camera can detect the radiation similar to a camera detecting light. Infrared cameras generally show hot areas as brighter and cooler places as darker. The amount of ambient light doesn't have an effect, so an infrared camera can operate in total darkness. Because of this property, the cameras are ideal for rescue operations underground and in smoke-filled buildings. They are also good for surveillance, victim locating, medicine, research and development, home inspections and of course in the military.
There are basically two types of infrared cameras: models with cooled or uncooled infrared detectors. Cooled models are bigger and more expensive, but take better quality photos than uncooled ones. Cameras come in various styles and sizes. Prices on them vary and they will generally cost you several thousand dollars at least.