I think recognising faces is just like the way that people say all the members of other races look the same.... Just in reality, everyone looks the same, even your own race. The only reason people don't usually say it about their own race is cuz they've seen so damn many of their own race...
The places where people look different are these very small things, subtle things like shape of jaw, shape of eyes, things that people who can tell the difference take for granted. They do differ between races but yeah, even among your own race it takes effort and wanting to be able to tell the difference before you get it. The differences between people are so small! People do actually all look really similar! I think it's like u just get a feel for it is the best way of putting it. I used to have some major problems as a kid telling certain people apart. Just, as time went by, it got easier because it bugged me and it was something on my mind.
Honestly, i think just wanting to tell the difference between people will make the difference. Just wanting it will make you think about it and just wanting it, even if it's not something that will come about overnight, it will actually solve your problem for you eventually.