I'll tell you something. Aspies are known for being able to discern differences, if anything. I think the problem with faces is desire and distraction. After all, on the face test, EVERYONE scored well above any chance, even if most scored poorly.
SO, it follows, if you try, you SHOULD be able to notice a difference, if there is one. With Kate and ashley olsen, their personalities, style, and hieght are different. ALSO, one had a weight problem. I couldn't begin to tell you which ones which, but I DO remember that. Unless they WANT to look alike, they will look different in a discernable way. Being a feature of "dual star", they often want to look alike though, or at least DID.
They might be flipping hamburgers at mcdonalds now if they weren't monozygotic.
The movie industry basically can't use young children in movies or films, because the laws make shoots nearly impossible. Shooting only one child in a monozygotic pair means they can shoot twice as long, and it relieves the problem. THAT is why the olsens even had a CHANCE! LATER, when they didn't have such big restrictions, one of the kids got to play the others cousin!
I doubt anyone expects anyone to easily tell monozygotic twins apart.
Steve