1. An image processing method applicable to a frame sequence comprising multiple frames, each frame comprising multiple groups of image elements, said method comprising the steps of: determining a global motion representation of image element property values representing a movement of corresponding image elements from a position in at least a reference portion of a reference frame to a different position in at least a portion of a frame; identifying, for a first group of at least one image element in said frame, a first reference group of at least one image element in said reference frame based on said global motion representation; calculating a first classification parameter as being representative of a difference in image element property values of said first group and said first reference group; identifying a second reference group of at least one image element in said reference frame based on a displacement vector associated with said first group; identifying a second group of at least one image element in said frame based on said global motion representation and said second reference group; calculating a second classification parameter representative of a difference in image element property values of said second reference group and said second group, said first classification parameter and said second classification parameter being indicative of whether said first group belongs to a foreground or a background of said frame; and providing a vector set comprising, for each group of image elements in said at least a portion of said frame, a respective displacement vector referring to a reference group of image elements in said reference frame of said frame sequence; wherein said determining step comprises determining, based on at least a portion of said displacement vectors of said vector set, said global motion representation, wherein a position-dependent global motion vector is determined based on said at least a portion of said displacement vectors of said vector set, wherein the position-dependent global motion vector is determined by estimating, based on said at least a portion of said displacement vectors of said vector set, elements of matrix A = [ a 11 a 12 a 21 a 22 ] and a vector b=[b 1 b 2 ] T by a least square method to determine said position-dependent global motion vector as having a formula: 
 v=Ax+b where v=[v x v x ] T is said global motion vector, v x is a first vector component of said position-dependent global motion vector in a first direction, v y is a second vector component of said position-dependent global motion vector in a second perpendicular direction, x=[xy] T is an image element position in said frame.