Quote Originally Posted by Abdula
It was stated early on that that was one of the abilities of the sharingan. Something to do with the sharingan's ability to see chakra.


Sounds good because if Sasuke was going to die or destroy the village then everything Itachi has done would have been for nothing.
Assertn is right, sharingan can see the difference between regular clones (bunshin no jutsu) and real user, but shadow clones (kage bunshin no jutsu) is a technique that's distributing chakra evenly to the clones and giving them a body. It is exactly because of this fact that sharingan CANNOT tell the difference, giving the sharingan user "just" the ability to see that the user has a body and see its chakra flow etc. therefore making it impossible to tell if a person is the real deal or a kage bunshin.

It is still possible to use common sense to get the idea which one is it, but sharingan is not the answer here.