Once only available to Hollywood and BBC weathermen, it’s now possible for anyone to use green screen or chroma key technology.
Chroma key is a technique for mixing two images or frames together, in which a color (or a small color range) from one image is removed (or made transparent), revealing another image behind it. This technique is also referred to as color keying, colour-separation overlay, greenscreen, and bluescreen.
This video was made using a couple of Sony HDD Camcorders, on one of them was screwed a 37mm adapter with a ring of green LEDs.
I sat on a sofa in front of a screen which is not green (but you can use green) but has reflective beads to reflect the green light back into the camera.
Using Apple’s iMovie 09 and switching on the Advanced Tools option in preferences allows you to add your green screen footage over existing footage.
There is a nice and simple guide on how to do that here.
Has quite a bit of potential to making short videos more interesting and adding learners and practitioners over existing footage to explain stuff.