{Designed by http://delphi.ktop.com.tw}
procedure TForm1.BitBtn1Click(Sender: TObject);
var DC,SourceDC,DestDC: HDC;
  bitmap:tbitmap;
  BHandle:thandle;
begin
  SourceDC:=CreateDC('DISPLAY','','',nil);
  DestDC:=CreateCompatibleDC(SourceDC);
  BHandle:=CreateCompatibleBitmap(SourceDC,Screen.Width,Screen.Height);
  SelectObject(DestDC,BHandle);
  BitBlt(DestDC,0,0,Screen.Width,Screen.Height,SourceDC,0,0,SRCCOPY) ;
  Bitmap:=TBitmap.Create;
  Bitmap.Handle:=BHandle;
  Bitmap.SaveToFile('c:\test.bmp');
  DeleteDC(DestDC) ;
  ReleaseDC(BHandle,SourceDC) ;
  bitmap.free;
end;