1. An image-encoding method, in which, when an image is transmitted and stored, an image frame is divided into processing regions with a predetermined size and encoding is performed while predicting a pixel value of each pixel for each processing region, the image-encoding method comprising: an object number-setting step of setting a number of objects in the processing region as an object number; an object pixel value-setting step of associating the objects in the processing region with object identifiers for identifying the objects, and setting one pixel value representing each object as an object pixel value; an object map generation step of generating an object map, which indicates an object in each pixel in the processing region by the object identifier, using the object pixel value; a reference object map-setting step of setting an object map, which is used when encoding a reference region which is an already encoded region around the processing region, as a reference object map; an object map-encoding step of encoding the object map using the reference object map; a predicted image generation step of generating a predicted image for the processing region by assigning the object pixel value to each pixel according to the object map; and an image signal-encoding step of performing predictive encoding on an image signal for the processing region using the predicted image.