this question should indeed get fucked.
I agree, but when you pose a problem to nerds, we can't help but propose solutions.
I live in a touristy area and I'm pretty sure his purpose is to charge costumers for photos (this is unbelievably profitable), as well as having them available for his own purposes. Here, we use those photos for advertising, but the OP is so vague as to make me think he's doing this for blackmail, porn or preventing customers from being able prove how bad his service actually is.
I know he wants to set up a expensive fix to bleed customers just a little bit or maybe get downright nefarious, but I still can't help but try to think of solutions:
Customer's won't wear anti-paparazzi gear to stop their selfies, but what if you plastered the interior of the vehicle with it instead? Low-lighting + bouncy ride will force them to use flash while your own high powered cameras, statically mounted in optimal points can do longer exposures and be positioned to be least affected by anti-paparazzi coatings and devices.
EMPs will only destroy cameras with moving parts that are very sensitive. I think you should still consider firing off small disruptive bursts of energy with every flash detected; expensive to create, but it seems your client is willing to go pretty far when it comes to screwing over his costumers, so don't discount them!
The post also isn't clear whether we are trying to prevent costumers from taking pictures of landmarks outside the bus, or the puke stains on the floor of the bus. We've clearly assumed the latter. But if you lock all the windows up, you can clearly put coatings or lighting on them to screw with photos.
Most of the other comenters recommended you re-look into IR. You didn't really say what failed, maybe the contractor you tested out just sucked? You might want to try that again with different methods.
On the off chance the client is not up to no good, add a sign that says: "You'll enjoy your ride better if you let us handle the photos!" Or if he'll just fess up that he's being evil, just TSA style search customers and confiscate cameras and phones prior to the trip.