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, wherein the step of establishing the latest background image by referring to the current image and the M images previous to the current image comprises: accumulating a redundant number of the first pixel in the previous I th image when a difference between the first pixel in the current image and the first pixel in the previous I th image is smaller than or equal to a first threshold, wherein 1≦I≦M; and serving the first pixel in the previous I th image as the first pixel in the latest background image when the redundant number of the first pixel in the previous I th image is greater than a second threshold, equal to the second threshold, or has a maximum value; 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.