Manipulation tutorials?

I was looking for a few of these not just for icons but namely larger graphics. I've been seeing them around GJ more and more and I've become addicted from afar and want to learn how to do them! Can anyone direct me to any manipulation tutorials which include but not limited to, maybe, transferring people from one picture to another, changing faces, etc. Some examples of what I'm looking for can be found here:

I saw a few REALLY great ones on GJ... these ones HERE and HERE and HERE.