Could there be an app for this? Apple is working on software that would disable an iPhone's video camera when used to film live events.
The software would work with infrared sensors at venues to sense when an iPhone is being held up to film something. The camera function would then shut down, preventing you from recording anything.
It would be quite a coup of Big Brother-esque proportions if Apple is able to get it approved - and those goons who film gigs on teeny iPhone screens directly in your line of sight could soon be a thing of the past.