I also would question why your trying to do this? Typically this is the type of thing game hacks do, which I am willing to guess is exactly what your trying to do.
But a quick google search produced the following: http://spazzarama.co...ct3d-api-hooks/
Copying screen buffer is not a hack, it does not change or automate any of the behaviour of the software, if doing that would be considered hack, then using things like fraps or any other screen recording software would be bannable offense.
I know about that spazzarma api hook, but its overly bloated with extra threads, and probably even changes running application by running CLR runtime host on it, and i dont want that. Also requires your assembly to be installed in GAC.