。
It's difficult to tell the real from the fake.
Literal
Genuine [and-と] fake [object-を] distinguish [nominalizer-の] [topic-は] difficult.
見分ける ('to tell apart by looking') is a compound verb — 見 ('see') + 分ける ('separate'). The nominalized verb phrase 見分けるのは ('the act of telling apart, as for it') paired with the formal adjective 困難 ('difficult') gives the line a measured, written feel — the same idea could be expressed casually with 難しい, but 困難 reads as more weighty and abstract.