On 21/10/2014 11:26, fred wrote:

On the scatter back problem, this doesn't happen as you will find there
is a foam grommet surrounding the lens in contact with the glass that
cuts out any internal or external reflections and the LEDs are (just)
far enough away and their beams narrow enough that external reflections
do not occur.


That sounds like a cheap camera.
All of mine have a tube which passes through the front glass to stop the
leds reflecting back from either surface.

An external IR illuminator is a better bet as that stops number plates
reflecting back and swamping the sensor.