1. An object detection method, comprising: sequentially receiving a plurality of images in an image sequence, wherein the images comprise a current image; establishing a latest background image by referring to the current image and the M images previous to the current image when the current image is received, so as to update one of N background images, wherein M and N are positive integers; and analyzing color models of the current image and the background images to determine whether a first pixel in the current image belongs to a first foreground object.