1. A method for detecting fog by use of a camera image or a video image, the method comprising the acts of: taking a two-dimensional image with at least one color channel or several color channels as a function of two independent location coordinates; determining a two-dimensional gray-scale function for the at least one color channel or for each of the several color channels, which defines a value of the gray scale as a function of the two independent location coordinates of the two-dimensional image; and performing a two-dimensional Fourier transformation of the two-dimensional gray-scale function depending on two independent frequency coordinates.