1. A method, performed in an apparatus, for updating a background model used for background subtraction of an image, comprising: receiving an image forming part of an image sequence, classifying a region of the image as foreground by performing background subtraction using a background model which comprises a collection of background samples for each pixel in the image, wherein the collection of background samples is arranged in a list of background images such that each pixel of the image has a background sample in each of the background images at a pixel position which corresponds to that in the image, and wherein the background images comprise background samples of images preceding the received image in the image sequence, replacing image contents in the region of the image which is classified as foreground by image contents of a corresponding region in a background image in the list, and adding the image to the list of background images by rearranging a collection of pointers which each points to one of the background images in the list, such that one of the pointers instead points to the image.