1. A predicted decoding method for decoding a bitstream data obtained by encoding a target image to be encoded referring to a reference image, the predicted decoding method comprising: (a) extracting from the bitstream data, coordinates point date indicating frame coordinates points of the reference image, coordinates number data indicating a number of the frame coordinates points and a compressed image signal related to a target image to be decoded; (b) selecting an image transformation parameter used for obtaining a predicted image, based on the extracted coordinates number data; (c) obtaining the predicted image from the reference picture, based on the selected image transformation parameter and the extracted coordinate point data; (d) obtaining a decompressed differential image by decoding the compressed image signal; and (e) reproducing a reproduced image by summing the predicted image and the decompressed differential image.