A method for decoding compressed image data recorded in an optical disk includes the steps of recording program data capable of performing partial decoding, in addition to the compressed image data, in the optical disk in advance; recording the program data temporarily in a memory card removably installed in an electronic device; recording the program data recorded in the memory card into a main memory within the electronic device; reading the compressed image data from the optical disk into the electronic device using a decoding unit arranged in the electronic device to decode the compressed image data partially; and decoding the partially decoded compressed image data by the program data recorded in the memory of the electronic device. The decoding method and the electronic device used to decode the compressed image data allow for future updates and improvements and real-time decoding.