1. An image processing method for an apparatus having an input unit that inputs an original image and a halftone processing unit that applies halftone processing to a predetermined area of the original image, the image processing method comprising processing for: selecting buried information; and shifting dots of a halftone pattern in the halftone processing according to the selected buried information, wherein, in the halftone processing, the shift of the dots is performed only in an area in which density is equal to or lower than predetermined density.