1. A method of determining a first motion vector of a current image block in a motion picture decoder, the method performed by a moving picture coding system and comprising: reading, by the moving picture coding system, a first image block providing a motion vector for deriving the first motion vector of the current image block; and determining, by the moving picture coding system, the motion vector provided by the first image block as the first motion vector of the current image block based upon reference picture index information, the reference picture index information indicating a type of reference picture for a co-located image block, the type being one of long-term and short-term, the type characterizing a temporal distance of the reference picture for the co-located image block with respect to the current image block.