^ No.
They cannot judge your speed by 'glimpse' They are not ninjas, we just assume the all are lol.
My advice to you, is to not open your mouth or deny everything until you see a speed camera reading.

"It looked like he was doing XXX" will not hold up in court. I know this through experience.

You are innocent until proven guilty.
First mistake everyone makes is admitting guilt before seeing the police officers evidence.
"Do you know how fast you were going back there ?"
"Yea about XXX over"

His got you.