질답란 검색해서 ..코드를 얻어서 구현하기는 했습니다..
그런데...이미지가 계속 중복되어서 나오다라고요...ㅎㅎ

for 문을 없애면 child 폼의 잔상이 계속 남아 있구요....
mdi 폼의 중앙에 한번만 나오게 할수는 없을까요?

procedure TFMain.ClientWndProc(var message: TMessage);
var
  DC: hDC;
  Row, Col: Integer;
begin
  with message do
  begin
    case Msg of
      WM_ERASEBKGND:
      begin
        DC := TWMEraseBkGnd(message).DC;
        if (Image1.Picture.Height <> 0) and (Image1.Picture.Width <> 0) then
        begin
          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);
        end;
        Result := 1;
      end
      else Result := CallWindowProc(FPrevClientProc, ClientHandle, Msg, wParam, lParam);
    end;
  end;
end;