Police will park nearby those cameras in unmarked cars. When someone runs the red light, They will get stopped by real police officers, and their license plates will be checked. If it's a forgery, they get jail time. When the kids learn that their friends are going to jail, they'll stop the practice or do it sparingly once they think police have stopped patrolling the area. It could become a problem that occurs occasionally.
I can foresee that people who actually do run red lights will tell the judge, "but someone forged my license plate!" How do you prove or disprove that you weren't their at that time? What little amount of evidence would you need?
The camera video quality will need to be improved drastically and have special light filters to remove windshield glare so they can get the faces of the driver and riders as well as the license plates. That will be expensive, but the best method for getting the best evidence at the scene of the infraction.