It's a bird, it's a plane, it's ... Christopher Reeve?
According to a GIF-poster who apparently possesses superhuman powers of perception, Zack Snyder spliced a frame or two of Christopher Reeve's face into "Man of Steel," at the moment when Superman takes off to fly through the World Engine. Check it out for yourself:
It's difficult to tell whether or not the "cameo" is authentic, especially since "Man of Steel" star Henry Cavill and Reeve already look eerily similar, and the sequence in question is somewhat obscured.
It also seems like a strange and potentially legally tricky bit of manipulation to do for what amounts to a one-second nod to the late actor and former "Superman" franchise heavyweight.
As skeptical as we are, Supes has taught us that anything's possible.