1. A method for decoding an image, the method comprising: determining whether both of a reference picture of a candidate block and a reference picture of a current block are long-term reference pictures, wherein the candidate block is from among a plurality of candidate blocks adjacent to the current block; when both of the reference picture of the candidate block and the reference picture of the current block are the long-term reference pictures, obtaining a spatial motion vector prediction candidate without scaling a motion vector of the candidate block; when both of the reference picture of the current block and the reference picture of the candidate block are short-term reference pictures, obtaining the spatial motion vector prediction candidate by scaling the motion vector of the candidate block; determining a motion vector prediction of the current block from among motion vector prediction candidates comprising the spatial motion vector prediction candidate; and generating the motion vector of the current block by using the motion vector prediction.