You mean...something like chroma key?

I think you should ask for help some big 3D FPS (first person shooter) game maker company (you can find them on the net..). They can help you to give solutions (e.g. 3D game software motor responsible for building complete body to stick figure and chop it for parts as well, or giving a deeper knowledge to do this).

I don't think so, I have never seen a SW able to subtract "knee", or "arm" or whatelse from a film or from an image

Dear David,

May I refer to Quake III Arena? If you know this game you observed what did I talking about. You have to see it: http://en.wikipedia.org/wiki/Quake_III_Arena

Dear Antonio,

Yes, something like that,

Dear Beres,

I think your mean is something like 3D stick figure?!! I know how to do that in a 3D space, I did that for my master degree. However, I will contact to the FPS game maker company. I am so grateful for your help.

You're welcome!

Dear All,

Finally I could remove a specific part of body in a video display.  It is possible and it is simple.