鎖屏狀態下,截屏圖片為白屏,還請高手指點

Question

本人在寫遠程控制程序時,遇到被控方鎖屏時,傳回來的圖像為白屏,且模擬鍵盤按鍵功能失效,模擬鼠標有效,還請高手提供解決方法.下為大致的截屏函數,還忘高手指點思路.procedure Tform1.CaptureScreen();
var
  Fullscreen: TBitmap;
  FullscreenCanvas: TCanvas;
  DC: HDC;
begin
  Fullscreen := TBitmap.Create;
  Fullscreen.Width := screen.width;
  Fullscreen.Height := screen.Height;
  DC := GetDC(0);
  FullscreenCanvas := TCanvas.Create;
  FullscreenCanvas.Handle := DC;
  Fullscreen.Canvas.CopyRect(Rect(0, 0, screen.Width, screen.Height),
  fullscreenCanvas, Rect(0, 0, Screen.Width, Screen.Height));
  FullscreenCanvas.Free;
  ReleaseDC(0, DC);
  Image1.Picture.Bitmap := fullscreen;
  Image1.Width := fullscreen.Width;
  Image1.Height := fullscreen.Height;
  fullscreen.free;
end;