The Japanese version of the 2004 Prius has an option for a rear-view camera and automatic self-parking. (Google for "prius camera parking" finds plenty of info about it.) The international versions of the car seem to be fairly standardized, so at least part of the software is probably there in the US version... which would be what you're seeing in the diagnostic mode.
Toyota makes a multi-display unit which combines the Nav, CD player and radio in one unit. This unit has a dedicated camera input which can be used to install a common camera to. The unit detects it and automatically displays it when the car is placed in reverse. However, this does not fit in the Prius.