1. An image decoding method comprising: decoding, from a bitstream including an image, information about a motion vector difference for a current block and information about a motion vector predictor for the current block; generating a motion vector predictor candidate group; modifying the motion vector predictor candidate group based on vectorial values of motion vector predictor candidates in the motion vector predictor candidate group; determining a motion vector predictor for the current block from among motion vector predictor candidates in the modified motion vector predictor candidate group based on the information about the motion vector predictor; and determining a motion vector for the current block based on the motion vector predictor and the information about the motion vector difference, wherein, the modified motion vector predictor candidate group includes a 1st motion vector predictor candidate and at least one of 2nd motion vector predictor candidates, the 1st motion vector predictor candidate is a motion vector of a collocated block to the current block, the collocated block is located in a reference picture, the 2nd motion vector predictor candidates are motion vectors of neighboring blocks of the current block, wherein the neighboring blocks include blocks located in upper left side, upper right side, and lower left side of the current block, wherein the modifying the motion vector predictor candidate group comprises modifying the motion vector predictor candidate group, when at least two of 2nd motion vector predictor candidates have the same value, by removing all of the at least two of 2nd motion vector predictor candidates except for one of the at least two of 2nd motion vector predictor candidates from the motion vector predictor candidate group, wherein the image is split into a plurality of maximum coding units according to information about size of the maximum coding units, the maximum coding unit is hierarchically split into one or more coding units of depths including at least one of a current depth and a lower depth, and wherein the current block is included in one of the one or more coding units of depths including at least one of the current depth and the lower depth.