The phrase “I’ve seen it all before” means that I’ve seen similar things in the past, and seeing another is not going to offer anything new to my experience. For example, if a friend said “Bill Clinton is having an affair!” I might reply “Yeah, I’ve seen it all before.”

So, with these Bardot photos, they’re saying that the citizens of Sydney have seen such behavior before, and they have literally seen the exact photos before.

While it might be a correct use of literally, it’s not a very good one, and certainly it’s unnecessary.