1. An image data processing method comprising: a step of storing an image data which includes a first image data related to a first object and a second image data related to a background or a second object which is different from the first object; a step of storing distribution information which indicates a probability of each pixel data being included in the first image data, with respect to at least one portion of the first image data; and a step of adding the distribution information when extracting the first image data from the image data.