I wonder if there is a subtle difference between "1" and "2".
1. I hardly know you.
2. I hardly recognize you.
"I hardly know you" This primarily means, I don't know you very well; we are not friends; I have only recently met you. It can also mean, "You have changed so much since I last saw you, I only recognise you with difficulty". In other words, the same as "I hardly recognise you".