Near IR is the 95% solution
Using 'The Art of War' for guidance*, play some *invisible to humans* / visible to cameras Near IR laser beams across the screen.
* use tactics such as:
Wait for the action climax of the film, then ruin it for the cameras
Or, using higher brightness fiddle with the cams' autoexposure time constant
Write anti-piracy messages on the screen
Saturate the market with inexpensive Near IR filters that don't quite work properly
By the way, such camcording is sometimes done *by staff*.
Myself? I just capture the new release 4K digital files sent by satellite to the digital theatres in Ireland and elsewhere (Kidding!!!! ...maybe...).