Disclosed are apparatus and a method for detecting cloud features. The method comprises: obtaining (402) image data (401); identifying (404) regions of the image data corresponding to a below-horizon region and an above-horizon region; classifying (404) one or more parts of the above-horizon region as a cloud feature; determining (409) an identification model specifying a visual appearance of some or all of the parts of the above-horizon region that have been classified as a cloud feature; and using the determined identification model, classifying (404), as cloud features, those regions of the of the below-horizon region whose visual appearance is as specified by the identification model.