7.2.12 background-image

(background-image CAM-ID [FILENAME])

Use the given image as the background of camera CAM-ID (which must be a real camera, not default or allcams). Centers the image on the window area. Works only with GL and OpenGL graphics. Use "" for filename to remove background. With no filename argument, returns name of that window's current background image, or "". Any file type acceptable as a texture is allowed, e.g. .ppm.gz, .sgi, etc.