Two points about the OP.
First, as Sera says, you could interpret 'in his own image' to refer to some other quality than mere physical appearance-- the ability to reason, for example.
Secondly, even if we take it to be true, that 'God made man in his own image,' refers to physical appearance, that statement is not mutually exclusive with the statement 'God made Clorx'ggrxegafka in his own image.' Even if man and some other alien species look totally different, those statements are compatible, because it is impossible to say "God has X and Y and Z physical traits and only X and Y and Z ."
Finally, how do you prove a religion to be true or false? Barring some bizarre supernatural phenomenon completely upending the laws of physics as we know them, or dying and appearing in some afterlife, it seems difficult at the very least to say "X religion is True" or "Y religion is False" with any sort of concrete proof behind the statement. Under normal circumstances, religion appears to fall outside the realm of proofs.