All photo editors use Photoshop these days, because aside from making basic touch ups a breeze it also makes it easy to radically alter a photo, perhaps a bit too easy for all those sloppy editors out there.
Whether they're changing a model's skin color, chiseling away at body contours or simply erasing someone or some thing from a photo entirely, it's easy for editors to make obvious mistakes when they're in a rush.
Even His Holiness the Pope can't prevent a Photoshop disaster from befalling one of his photos, unless this mysterious third leg is actually one of the Vatican guards going full ninja mode...