A method for decoding an image according to the present invention comprises the steps of: receiving and parsing a parameter set including indication information which indicates the presence of withheld information to be used in the future; receiving and parsing a slide header including the withheld information, when the indication information indicates the presence of the withheld information; and decoding the image according to semantics and a value corresponding to the withheld information. As a result, provided are a method and an apparatus for describing an additional extension information indication in a bitstream supporting a hierarchical image.