1. An image prediction method for obtaining a predictive image from an object-based reference image having at least one object image, including a luminance signal expressing each pixel value, and a transmittance signal expressing the transparency of each pixel, said method comprising: obtaining substitute pixel values for each pixel located outside the object image in a predictive subarea of the reference image by referring to a pixel located inside the object image, the predictive subarea adaptively selected for a target subarea from the reference image; and generating an optimum predictive subarea by substituting the substitute pixel values into the predictive subarea for the pixels located outside the object image.