Atmospheric visibility, or meteorological visibility, is an important information for high-stake applications, such as transport safety and air quality. It is normally monitored by means of dedicated optical sensors, but those are rather expensive, and are thus deployed on a limited number of sites considered critical (such as airports). As a consequence, major efforts have been devoted to the development of methods to monitor the weather, and more specifically to monitor the atmospheric visibility, with surveillance cameras, because they are ubiquitous and can serve several purposes. One problem which always arises when working on such a method is that of validation, because reference data is not easy to come by. That is the reason why the Ifsttar (which later became the Université Gustave Eiffel) collaborated with Meteo France in 2009 in an effort to collect outdoor images associated with meteorological optical range and sky luminance data, in order to test their own camera-based visibility estimation methods.