As if the prequels couldn't get any worse or have any more unnecessary CG, it looks like George Lucas might've used takes of different actors as Anakin in the same shot, and then morphed them all together so you wouldn't notice. Ten years after the film came out, Redditor rod_munch spotted the trick and posted a GIF of Anakin clearly morphing (not from Skywalker into Darth Vader, but into different versions of himself).

For reference, this is what Anakin Skywalker looks like for most of the movies:

Sources: Reddit