1. A sky detection system that detects sky in an image collection device, the system comprising: an image collection unit that collects information of a color image; a color-feature extraction unit that extracts a color feature of each pixel from the collected image; a distance measurement unit that measures a distance between said each pixel of the collected image and a lens; a first classification unit that classifies said each pixel of the collected image as either a sky pixel or a non-sky pixel based on the color feature; and a second classification unit that further classifies said each pixel of the collected image as either the sky pixel or the non-sky pixel based on the distance and a result of the first classification unit.