Check out JhowT.net for future info and material!
Creating clean plates is something visual effects artists need to do all the time. The guesswork in cleanly creating & aligning one, however, can sometimes be difficult.
In this video we talk about an easy way to take the 'guessing' on what frames can be helpful in generating a clean plate, and -- more importantly -- how we can be positive that they are aligned correctly before we begin splicing everything together.
We simply refer to this as the 'neutral gray method'...but whatever you choose to call it, be sure to add it to your bag of tricks. :)