In one embodiment, the method includes obtaining reference picture information, and determining at least one reference picture of the current image block from the reference picture information. The reference picture information indicates a reference picture type of the reference picture. The reference picture type is based on temporal distance between a current picture including the current image block and the reference picture. At least one motion vector of the current image block is obtained according to the reference picture type. This obtaining step includes obtaining a motion vector of a co-located image block, and generating the motion vector of the current image block based on the motion vector of the co-located image block and the reference picture type. The current image block is decoded by motion-estimating the current image block using the motion vector of current image block.