Abstract. Characterizing the atmosphere is one of the most complex studies to undertake due to the non-linearity and phenomenological variability. Clouds are also amongst the most variable of the atmospheric constituents, changing their size and shape over a short period of time. There are several sectors in which the study of cloudiness is of vital importance. In the renewable field, the increasing development of solar technology and the emerging trend for constructing and operating solar plants across the earth's surface requires very precise control systems that provide optimal energy production management. Likewise, airports are hubs where cloud coverage is required to provide high-precision periodic observations that inform airport operators about the state of the atmosphere. This work presents an autonomous cloud detection system, in real time, based on the digital image processing of a low-cost sky camera. The system's overall success rate is approximately 94% for all types of sky conditions.