I want to make a short film using stuff that has aleady been filmed

I want to take a film clip and pull the actors off of it and then place them in other film clips.

Like in photoshop how you can trace out a person leaving only that person and then you can place that person in another picture- yes I know it's a whole other ball game when dealing with moving images like in video.

and the clips I am using I would evan have a hard time telling a program to just get rid of this color or that and just leaving the people since the people are in the woods and alot of the colors on them are also in the backgrounds.

I am hoping that there is a way to do this other than frame by frame.


Ps on a whole other note, my next thing I will have to work on is pulling a texture off of a film monster and putting it on a 3d studio max monster.