Just talked to a colleague working with me. He recently contested a driving violation (speeding ticket) and won.
He had been given a ticket for speeding (58km in a 50 zone). He then took a camera, took a few photoes from the speed limit sign which was blocked by some branches from a tree in the area where he got the ticket. The judge cancelled the fine.
If you decide to contest, you must gather as much evidence as you can.