title: Detect when users take screenshots of my program
body: <p>I'm writing a Windows application. How can I tell when a screenshot is being taken of it? I read about how to detect the hotkey being pressed, but I'm more worried about the case where every 100 ms or so another program is taking screenshots of it. Namely, I'm trying to notice when someone creates another program (say a python one using ImageGrab, as mentioned in another post) which constantly takes screenshots of my app and uses them to read info off of it.</p>
  
  <p>I don't care much about preventing the screenshots from being taken - I can just ban the user once this behavior is noticed.</p>
  
  <p>Is this possible? Is there a windows message sent when any app takes a screenshot, like with WM_HOTKEY? Or does windows just use the latest info from the latest paint events, and return that to the other program directly, without my app being able to notice at all?</p>