1. An apparatus for decoding an image, the apparatus comprising: a reference picture comparer configured to determine whether a reference picture of a current block and a reference picture of a candidate block are the same, wherein the candidate block is from among a plurality of candidate blocks adjacent to the current block, and when the reference picture of the candidate block and the reference picture of the current block are not the same, determine whether both of the reference picture of the candidate block and the reference picture of the current block are long-term reference pictures; and a motion vector determiner configured to, when both of the reference picture of the candidate block and the reference picture of the current block are the long-term reference pictures, obtain a spatial motion vector prediction candidate without scaling a motion vector of the candidate block, determine a motion vector prediction of the current block from among motion vector prediction candidates comprising the spatial motion vector prediction candidate, and generate the motion vector of the current block by using the motion vector prediction.