Fixable by taking a picture of every opticom user?
That being said, this is kind of a non-issue already, I have heard a story about someone abusing the preempt sensors like 10 years ago and never since then. Maybe there already exists an encoding scheme.
IMO a huge majority of people realize how illegal it would be to mess with these things, and the risk/reward is very low. Anyone who would take that risk would probably just run a red light instead.