How does Nikon bring up pure white photos in a small photo box?

I'm afraid the "small camera box" you mentioned is a kennel soft box. The background of this soft box is usually white, but it will change with the color temperature of the selected lighting. Nikon's high-end card machine and most SLR cameras have the option of "preset white balance". You can get photos with pure white background by determining the color temperature of the light source when shooting on white background. Please refer to the user manual to learn how to preset.