The photographer denies that it is a trained wolf. What can he do to show he's right, the accusation wrong?
It's extremely hard, nigh impossible to prove that something is not the case (which is why conspiracy theories are so abundant and hard lived.)
Suppose he produces Ossian, compares that wolf to the one in the photo, and demonstrates thus that it isn't. Isn't proof that it isn't a (different) trained wolf anyway. (Nor, i'm sure many will argue, that it isn't Ossian. Why, it could be Ossian in disguise! ;))