Is there a free green screen image maker/editor. I need something to put an image on a green screen on my...?

movie maker projects/videos. I'll take any virus-free freeware, torrents, seeds, or effects things. I just wanna be able to put like a picture behind me while I'm talking or put a video of godzilla so I can act all scared. That would be cool and links would be appreciated or just the url. Easy ten points...