speed = distance/time therefore "counting the lines" effectively gives what you are calling a "secondary visual evidence" crap....
I think you ought to refrain from calling it "crap" now, as you have just stated, it is fact. Without the lines on the road, the rear facing camera's couldnt be used to prosecute someone. Well in theory they could, but it wouldnt hold up in court too well.
Its true that I didnt know how the front facing cams worked, but then I bet there isnt many people who do. I was basically referring to what I do know, which is that the lines are needed on the usual camera's one see's out and about, to prove that you were doing above the speed limit.
Theres a million and one loopholes in the law, there isnt anything (general road offences) that a specialist (and may I add expensive) lawyer can't get you off for. This is why so many celebrities and footballers etc get away with traffic offences without even points in most cases, because they hire the very best lawyers in the business and there is always loopholes in almost everything.
This was exposed big time by the Tonight programme on ITV just last year.