I find it difficult to tell friends from the enemy.

This is a common problem for new OFP players. It will take you time and experience for your eyes to recognize the distinctions between NATO, Russian and resistance uniforms, helmets and weapons.

Of course, at distances, discerning between friendlies and enemies remains a problem but that's true in real life as well, isn't it? That's why it is always beneficial to get hold of a pair of binoculars.