1. A smoke detection method for identifying, in a current input image, an area indicative of a presence of smoke, there being a sequence of two or more input images, said method comprising: initializing a background estimation as one of said input images; comparing said current input image with said background estimation to detect a partial obscuring of said background estimation indicative of the presence of smoke in said current input image; forming an estimate of a color of and a degree of said partial obscuring of said background estimation in dependence on said current input image and said background estimation; updating said background estimation in accordance with said current input image and said background estimation; and forming a reconstructed background from said current input image, said estimate of said color of said partial obscuring of said background estimation and said estimate of said degree of said partial obscuring of said background estimation, said updating said background estimation comprising forming a linear combination of said current input image, said background estimation and said reconstructed background estimation.