In Week #13 of TBT for 52 Weeks I discuss color keying, cropping, and rotoscoping.
Week 13 of TBT for 52 Weeks - Color Keying
Week 11 of TBT for 52 Weeks - Cropping
In Week #11 of TBT for 52 Weeks I talk about using cropping as a video editing technique to duplicate yourself into a scene multiple times.