1. A method for detecting a background in an image selected from a plurality of related images, each formed by a set of pixels, and captured by an imaging device, this background detection method comprising the steps of: establishing, for a determined pixel position in said plurality of images, a background history comprising a plurality of addresses, in such a manner as to have a sample pixel value stored in each address; comparing the pixel value corresponding to said determined pixel position in the selected image with said background history, and, if said pixel value from the selected image substantially matches at least a predetermined number of sample pixel values of said background history: classifying said determined pixel position as belonging to the image background; and updating said background history by replacing one of its sample pixel values with said pixel value from the selected image; and characterized in that: the address of the sample pixel value to be replaced is randomly chosen.