FIGURE 2.—The factors which reveal vehicles to enemy aerial observation and which must be concealed or camouflaged are illustrated above. Aerial observers and photo interpreters are able to locate vehicles and often to identify their types, number, and intentions by detecting the presence of one or more of these factors. Even where the color of the vehicle is similar to its surroundings, the "value," or difference in lightness and darkness between them, may indicate the presence of the object. In an ordinary photograph, "values" indicate the presence of objects that are differently colored. When it is impossible to make a vehicle the same color as its surroundings, much is accomplished if the lightness or darkness of the vehicle is made similar to the surroundings.