title: Take screenshot of desktop when Windows is locked (Win+L)
body: <p>I want to take a screenshot of desktop while Windows is locked (with Win+L). Standard methods make a black screen, with code of pixel:</p>
  
  <pre><code>COLORREF color = GetPixel(hdc, x, y);
  </code></pre>
  
  <p>equal -1. Neither a user mode program nor a service could capture a useful image. Any ideas?</p>