在python中截取一个应用程序，无论它在前面是什么

So I can use PIL to grab a screenshot of the desktop, and then use pywin32 to get its rectangle and crop out the part I want. However, if there's something in front of the window I want, it'll occlude the application I wanted a screenshot of. Is there any way to get what windows would say an application is currently displaying? It has that data somewhere, even when other windows are in front of it.So I can use PIL to grab a screenshot of the de