usually by icon untilll they change it but somtimes i go by username it matters

Normally it's both....

depends on if there's another person I know with the same icon or close to it. Normally though, it's by username.

Okay my name was just something my bff said (read and watch A LOT of vampire books/tv-shows...

They change their icons so user names is better but some have a fixed icon so maybe both

Pretty much.

Usually their username as they dont change that:)

i'm not sure

Not sure...Neither?
I add people who are nice and share the same interest as me. And if someone fans me, I fan back.
But if I have to choose between a person's profile photo or username, I say photo. After all, "A picture is worth a thousand words".