Compare function's result of PIcture is not unique

Hi there,

    When I test below function, Pict1 and Pict2 are totally different, but sometimes it gets 'Same', sometimes it gets 'not same', Please guide me why the compare result is not unique. 

function Test1()
{
  Pict1 = Utils.Picture;
  Pict1.LoadFromFile("X:\\XXX\\img.png");

  if (Pict1.Compare(Pict2))
  {
    Log.Message("Same");
  } else {
    Log.Message("Not Same");
  }