As in, how do you know if your friend isn't a fake and is the real one? And vice versa I don't know how to explain it in the title so if someone could like. Correct me or something.

Me and my friend sings "What is love" if we're suspicious of being a fake. If she or I doesn't reply the right answer then she's probably a fake.

How do you and your friend know who's the real who? o: (dunno if that makes sense)

Dates of birth and name

I ask them “What’s my Dog’s name?” If they answer wrong then theyre not my real friend

Heh, it’s fairly hard to guess...

I demand photographic evidence of my friends whenever they start a new conversation with me. If I don't reply for about 10 minutes, they know it's me.

Well, its fairly hard to know for certain, but its usually easy to guess by the way they type. For example, I've got a friend who uses the word "between" weirdly. "Between, do you know -insert text here-" She uses the word "between" as a way to change the topic. She also uses a mass amount of smileys... whenever I'm idle or have not replied her for a while when I haven't told her why beforehand, she starts making what she calls a "smiley pyramid" as a source of entertainment until I get back.
(Below is a smiley pyramid, for those who are confused!)
:)
:) :)
:) :) :)
:) :) :)
etc.

Then there's the friend who constantly text types and starts off each and every chat we have online with "hey la" or yo". I don't know anyone else who starts a conversation this way haha.

As for me, I suppose I do use the word "haha" a lot, not sure when that started, but anyway. I joke a lot as well, though a really bad comedian at that! (Only a few of my closest friends ever get my jokes!)

I've never really thought about this question: it never occurred to me that anyone would want to pretend to be a friend I know;I never really thought about anyone I'm talking to of being a 'fake', and perhaps that's a weakness on my part - too trusting! But if I'm ever suspicious, I guess there's always the method of asking things about them that I know the answer to!