A method for detecting fog by use of a camera image or a video image includes the taking of a two-dimensional image with at least one color channel or several color channels as a function of two independent location coordinates. The method determines a two-dimensional gray-scale function for the at least one color channel or for each of the several color channels, which defines the value of the gray scale as a function of the two independent location coordinates of the two-dimensional image. Then, the method performs a two-dimensional Fourier transformation of the two-dimensional gray-scale function depending on two independent frequency coordinates.