Rules of Evidence

The cop cannot relate any information that was said by someone else. That is called hearsay and is inadmissible. For example, if the cop checked on the computer that your licence was suspended he cannot testify to that. The information was gathered by someone else and put on the computer. The prosecution has to provide a certified document from the Ministry of Transportation proving your licence was suspended.

A witness cannot give an opinion unless it is general knowledge or they are an expert in a particular field. If the cop visually estimated you were speeding, they have to establish they are capable of making such estimation.

Circumstantial evidence is different from direct evidence. A video of you smashing into the back of another vehicle is direct evidence. Another video of your car at the scene of an accident is circumstantial. It only shows that your vehicle was there, not whether you caused the accident.

Probative evidence must be material and relevant. Materiality should not be confused with relevance. If something is "material" it means it matters to the case, it has some logical connection to the outcome of a case or some proposition or fact scenario. For example, in a speeding trial, the operating state of your speedometer and its' repair history is material to the trial. Whether you have cloth or leather upholstery is not.

Evidence is relevant if it tends to support or weaken a proposition. A mechanic's report on your speedometer is relevant if you are arguing the speedometer was broken. If you are arguing that the cop pulled over the wrong vehicle, then the mechanic's report is not relevant at all.

Thus if you are arguing you didn't know you were speeding, then the condition of your speedometer is material and the mechanic's report is relevant.

Objections

If a witness breaks the rules of evidence above, stand up and say "Objection, hearsay," or "unsubstantiated opinion" or "leading question", or "what is the relevancy?".

Sometimes the justice will allow the evidence but give it a diminished "weight". That is, he will consider it along side other evidence to determine what is credible and more likely to be believed.