procedure TMDIChild.Button1Click(Sender: TObject);
var
  ScrInfo: TScrollInfo;
begin
  fillchar( ScrInfo, SizeOf( ScrInfo ), 0 );
  With ScrInfo do
  begin
    cbsize := SizeOf( ScrInfo );
    fmask  := SIF_ALL;
    GetScrollInfo( ImageEnView1.handle, SB_VERT, ScrInfo );
    ShowMessage( IntToStr( nPos ));
  end;
end;