procedure TForm1.Button1Click(Sender: TObject);
var DCDesk: HDC; // hDC of Desktop
  bmp: TBitmap;
begin
  {Create a bitmap}
  bmp := TBitmap.Create;
   
  {Set a bitmap sizes}
  bmp.Height := Screen.Height;
  bmp.Width := Screen.Width;

  {Get a desktop DC handle - handle of a display device context}
  DCDesk := GetWindowDC(GetDesktopWindow);
  
  {Copy to any canvas, here canvas of an image}
  BitBlt(bmp.Canvas.Handle, 0, 0, Screen.Width, Screen.Height,
         DCDesk, 0, 0, SRCCOPY);

  {Save the bitmap}
  bmp.SaveToFile('ScreenShot.bmp');

  {Release desktop DC handle}
  ReleaseDC(GetDesktopWindow, DCDesk);

  {Release a bitmap}
  bmp.Free;
end;

procedure TForm1.Button1Click(Sender: TObject);
begin
  Timer1.Enabled := True;
end;

procedure TForm1.Timer1Timer(Sender: TObject);
var DCDesk: HDC; // hDC of Desktop
  bmp: TBitmap;
begin
  {Create a bitmap}
  bmp := TBitmap.Create;

  {Set a bitmap sizes}
  bmp.Height := Screen.Height;
  bmp.Width := Screen.Width;

  {Get a desktop DC handle - handle of a display device context}
  DCDesk := GetWindowDC(GetDesktopWindow);

  {Copy to any canvas, here canvas of an image}
  BitBlt(bmp.Canvas.Handle, 0, 0, Screen.Width, Screen.Height,
         DCDesk, 0, 0, SRCCOPY);

  {Save the bitmap}
  bmp.SaveToFile('ScreenShot.bmp');

  {Release desktop DC handle}
  ReleaseDC(GetDesktopWindow, DCDesk);

  {Release a bitmap}
  bmp.Free;
end;
procedure TForm1.Button2Click(Sender: TObject);
begin
  Timer1.Enabled := False;
end;