realtime image processing

Is it possible, to, with a high FPS, have realtime image processing, processing each frame coppied into an image?

What I mean is, could it be possible to have each frame in a game be captured into an image (using copyrect?), edit the image as wanted, and display it on the monitor?
(a sprite in front of the camera would work, I've already got a system for that, basic things like a primitive motion blur and heat shimmer; what i really need is the fast image editting)

any help is largely appreciated

I've found that the biggest time in something like this is copying from the backbuffer to the image...unless you are doing per pixel calculations :). Try to keep the graphics size down to really small resolutions like 320×240 and you might be able to pull it off. Also kind of defeats the purpose :)

half-life 2 does it (realtime per-pixeling), so, there's gotta be a way, if not in blitz, in userlib.