There are provided a method and apparatus for forming a three-dimensional image. The method and apparatus form an arbitrary colored image on the surface of a thermally expandable sheet by using surface image data. The method and apparatus form a mirror image, of which the density of a black component is adjusted in consideration of the influence of the density of the colored image on a bulge height of a thermally expandable layer so that an originally scheduled bulge height can be achieved, on the back of the thermally expandable sheet. The method and apparatus can achieve an intended bulge height by expanding the thermally expandable layer with thermal energy that is generated in the mirror image and the colored image when the thermally expandable sheet is irradiated with light including infrared wavelengths from the back of the thermally expandable sheet.