The invention concerns a system and method for detecting, at night, the presence of an element such as fog interfering with the visibility of a road scene situated in front of a vehicle, comprising the following operations: acquiring an image of the road scene, extracting, from the image of the road scene, at least one light halo produced by a lighting device of the vehicle, approximating a form of this light halo by an elliptic curve, comparing the form of this light halo with the elliptic curve obtained in order to deduce therefrom the presence or absence of an element interfering with visibility.