An artificial intelligence (AI) decoding apparatus includes at least one processor configured to execute one or more instructions to: obtain a second image corresponding to a first image by performing first decoding on image data included in a main bitstream, obtain AI upscaling activation flag information included in AI data of a sub-bitstream, determine whether to perform AI upscaling on the second image, based on the AI upscaling activation flag information, when it is determined that AI upscaling is to be performed on the second image, obtain a third image by performing AI upscaling on the second image, through an upscaling deep neural network (DNN) set according to upscaling DNN information, the upscaling DNN information selected from among a plurality of pieces of pre-stored upscaling DNN information based on at least a portion of the image data and/or at least a portion of AI sub-data.