Found answers myself!
The easiest way to do this is to activate the window and to send an
Alt-PrtScr keypress event. After that you can simply read the captured image
from the clipboard. How to send a printscreen or alt-printscreen is explained
by me in this thread on EE on using SendKeys.
To find the window of a particular application, this link will help,
To capture the screenshot of the whole screen or a particular are, this will
Once you obtain the handle to the application, find its location and
dimensions and capture the image of that area.