This type of image shows heat based radiation from the infrared spectrum. In other words, the warmer the surface, the more infrared radiation it emits. For a satellite image, cooler surfaces are bright and warmer surfaces are dark. Since the atmosphere cools as you increase in altitude, clouds would show up as bright areas and land surfaces as dark areas. In addition, low clouds will be more gray and higher clouds will show up more white. Tall thunderstorm clouds will show up as bright white and fog will be hard to discern from land areas. A large advantage of IR is that you can view it 24 hours a day.