Below is a series of images that will help with camera positioning when using a camera for an ANPR application.
In the United Kingdom it is recommended to have the ANPR camera read the rear number plate. Rear number plates are usually illuminated and are less reflective than the front number plate. Also the detecting rear number plates will alleviate glare from the vehicle headlights and the camera IR illuminator which can blind the camera if positioned incorrectly.
For other countries please check with your local LILIN branch for recommendations as each countries number plate requirements are different.