"Difference Key"

[armadillo]

What program would I consider for implementing a difference key?

http://en.wikipedia.org/wiki/Keying_(graphics)

I can't find it in Final Cut.

Is it possible to implement a difference key in a moving shot?

 

[mahklo]

After Effects, or Digital Fusion...etc

 

[armadillo]

Well I have found a "Difference Matte" in FCP but when I use it, all it does is turn the whole clip black. Is this feature non-functional in FCP?

Thanks

 

[vtbpro]

Combustion as well!!!!