Capture image of a specific window.

[sakishrist]

Hello all!
I need some way of getting the image of a window outside my program. You may say that's easy with just finding the position of the window and then cropping down a full screen captured image to the size and position of that window. But here comes the problem: what happens if the window is under an other window, part of it is not visible or it is hidden? Note that i don't want to make it get the focus or be visible (if invisible). let's say i find the hwnd of the window that I want to get its image and then is there any command i can send to it with the SendMessage function or is there some other way to capture the image?
I appreciate any idea you may have!