Mobotix has released sensors with LPF for capturing license plates on several different models.  While the M12 has had an LPF option for many years, the D14 and S14 now have it available and give you much greater flexibility than you have with the M12.  LPF is used in combination with an IR illuminator to allow for license capture.  It is difficult to do this without LPF because head or tail lights are to bright for a camera to adjust in time to get the plate.  IR with LPF effectivly blocks this light and picks up only the reflectivity of the plate.  Simon Hall over at MxInstaller has written an excellent guide on how to configure a Mobotix camera for the highest accuracy.  A link to it can be found here:

How To Setup For Automatic Number Plate Recognition With MOBOTIX