Those are called Bullet cams. Kind of expensive I think, but probably cheaper now. All you need is the chip. Those camera's are small and some of those "security or spy" business's carry the chip (which is the camera) and the wires to plug them into any device that will record the video signal, or a wireless sender that can then be picked up by any device (laptop) that can record the signal. These chips are used to make home made security camera's. You know, in your clock or pictures or books so you can spy on the babysitter or whatever.
I think those are kind of cheap and you can embed them in a shield or on a headband.
I used to tape this palm sized digital camcorder on my helmet when playing paintball. It was hard to adjust to get a good pic because I couldn't see it but the pics were sometimes very interesting. If you had a chip that was "sending" the image someone could make sure you were getting the frames you wanted.
One SCA guy did have a camera in his shield and took "shield cam" pics. Don't know whatever happend to those. Might google "shield cam" and see what pops up.
Konradr