Of course it is NOT illegal to use portable video equipment in an aircraft.

If it was permanently mounted that is something else, in terms of paperwork.

Powering it from say the cigar lighter is OK too. If the aircraft electrical system was modified to bring out power sockets to plug things into, that needs a signoff, and perhaps a load analysis.

People make such simple things so complicated.

What I wonder is whether anybody has yet mounted a camera externally, by attaching it internally (e.g. with suction cups to the internal surface of the window) and having it poking out through the little opening window which many planes have. That would avoid the usual cockpit reflections and would be a simple solution to both the practical and the legal issues.

BTW, large chunks of this thread seem to have gone missing.

From my own experience I don't believe filming in the air is worth the trouble. A suction mount on the rear side window works well, but then you only have one angle - yours truly at the controls and perhaps the runway when on final approach. The headcams move around too much. May be ok as a record but I wouldn't torture any third party into watching it. Another camera pointing at the scenery is a good idea but really you need to have someone film from another aircraft to capture what is happening aerodynamically. It all gets very boring after a while - better just to enjoy the moment (if you can while the instructor is screaming at you :}). Still photographs are another matter and often have a unique beauty all of their own.

you could use a helmet mounted cam, might fit onto headset otherwise im sure there are different mountings including suction cups etc. These things are light (seen footage from an army patrol in Afghanistan using such equipment). Take a look at this website - I am looking into this as well for various applications
Helmet camera bullet cameras from dogcamsport

You don't want a camera that moves every time your head moves! I thought we were talking about "film making"? Watch some TV/DVD/film/anything and notice how little the camera moves. Compare this with footage taken with a headcam on You Tube etc. Awful!