I think by the letter of the law in the UK there are a few of them you could challenge if you know where your caught....
I think a camera in the UK has to be conspicuous and easily seen. I quashed 1 attempt of getting points put on my license in the North a few years back by prooving the copper was hiding behind a tree.....
Copper was repremanded and altho i was actually speeding they let me off with it in court....