The NHW11 (US 2001-2003 model years) model Toyota Prius does not have a rear view backup camera from Toyota available. There is a third-party unit available, though:
http://coastaletech.com/viewtech.htm
The rear-view backup camera on the current model of Toyota Prius, the NHW20 (US 2004-current model years), is not standard. It was not available on the 2004-2005 model years - it was a new option beginning on the 2006 model year (minor redesign that year).
http://pressroom.toyota.com/Releases...T2005092058045
Base model or optionless 2006-current Toyota Prius do not come with the rear-view backup camera. You need to get a higher option package to get the rear-view backup camera, but most dealers order one of these optioned Prius as their "base" model.
http://www.toyota.com/prius-hybrid/options.html
There isn't an available accessory from Toyota to add the rear-view backup camera, but on some Toyota Prius owner's groups I have heard of some people attempting the retrofit by ordering and installing the missing parts themselves. See:
http://autos.groups.yahoo.com/group/Prius-2G/
http://autos.groups.yahoo.com/group/2009-Prius/
http://autos.groups.yahoo.com/group/toyota-prius/
http://www.priuschat.com/
http://www.priusonline.com/
to check in with other Toyota Prius owners. Check their message archives and you'll find a few retrofits.