Как сделать родительское окно с фоновым рисунком в клиентской области

FClientInstance: TFarProc;
FPrevClientProc: TFarProc;
procedure ClientWndProc(var message: TMessage);

procedure TMainForm.ClientWndProc(var message: TMessage);
var
  Dc: hDC;
  Row: Integer;
  Col: Integer;
begin
  with message do
    case Msg of
      WM_ERASEBKGND:
      begin
        Dc := TWMEraseBkGnd(message).Dc;
        for Row := 0 to ClientHeight div Image1.Picture.Height do
          for Col := 0 to ClientWidth div Image1.Picture.Width do
            BitBlt(Dc, Col * Image1.Picture.Width, Row *
            Image1.Picture.Height, Image1.Picture.Width,
            Image1.Picture.Height, Image1.Picture.Bitmap.Canvas.Handle,
            0, 0, SRCCOPY);
        Result := 1;
      end;
      else
        Result := CallWindowProc(FPrevClientProc,
        ClientHandle, Msg, wParam, lParam);
    end;
end;

FClientInstance := MakeObjectInstance(ClientWndProc);
FPrevClientProc := Pointer(GetWindowLong(ClientHandle, GWL_WNDPROC));
SetWindowLong(ClientHandle, GWL_WNDPROC, LongInt(FClientInstance));