The speed cameras in Oensingen don't take rear photos, at least when they came into operation a couple years back (source). The police says that they randomly make mobile tests there to catch speeders on motorbikes too. The Oensingen cam is advanced in another regard. The photos are of such a good quality that the driver can be identified and if the driver isn't wearing the seat belt or operating his cell phone without hands-free car kit, an additional fine will be slapped on top of the speeding fine.

Modern speed cameras take photos from front and rear. The tech specs of one of the common cameras at Swiss roads can be downloaded here. They measure with laser and the measurement isn't necessarily at the same place like the camera.