This one, I think, I am likely to struggle with. The easiest distinguishing feature from the ubiquitous Small White, is at the apex of the forewing, where this species differs by virtue of the lack of of a fork in vein 7. 

Therefore, one would have to be very keen to obtain butterfly photographs of enough Small Whites to be sure. I think this shot is accurately identified!- it was flying with several others in Southern Italy, September 2019.