Parking tickets should be backed up with photographs anyways, taken by the ticket-writer.
There's hundreds of years of jurisprudence based on the idea that an eyewitness account of an alleged act, delivered by a person bound by oath to be truthful, can be accepted by the court as evidence supporting the alleged act. Why would you want to reverse that?
Taken to a logical end, wouldn't this also mean that rapists, murderers, and kidnappers would walk free if none of the witnesses to their crimes happened to have a cameraphone handy at the right moment?
If you get ticketed, you're always free to take your own photographs of the scene and bring them to court with you when you contest the ticket.