It depends on the court rules and legislation in your area.
Please do some research. Don't assume that these cameras mean an open-and-shut case against you. You can trash the tickets in certain Southern California areas with much risk or reprisal. I read an article this spring that said Los Angeles County made it a bottom priority. That is because a lot of people were not paying and the tickets were too costly to pursue. It was too tough for them to meet the 6th amendment requirement.
Here are some excerpts from the legal publisher NOLO. Note that they are commenting on red light tickets, but a lot applies to other camera tickets.
At a trial, the government (whether represented by the police officer or a prosecutor) must present evidence on how the device works and that it was working properly on the day the citation was issued. The prosecution must also present the camera’s photos showing the vehicle’s license plate and the driver, along with the driver’s license photo of the vehicle’s registered owner.
If the images are clear, you can consider mounting the following defense: If no employee from the company that maintains the red light camera device shows up to testify, you should object to the photos being admitted into evidence, saying, “Your Honor, since no one has appeared to authenticate the photographic evidence, I object to such evidence for lack of foundation.” If the photographs are excluded, there is no evidence to convict you.
Source in comments.