My digital SLR camera, a Nikon D50, is able to detect infrared light. Using an infrared filter, I can take photographs of that light. Since infrared radiation is put out by heated objects, the resulting images tend to show the trees and grass brightly, but water and the sky is dark.
An IR filter cuts out almost all visible light, so a tripod is needed. In this pair of images, I took two pictures from exactly the same spot, one with the IR filter on, and one without.
Some time ago, I talked about how the infrared images come out of the camera in a monochrome red. In all of these pictures, I converted to black & white. Here are a couple more: