On the one hand, if you created the photograph, you are presumed to have copyright. On the other hand, it may be very difficult to prove your copyright is enforceable in a court of law.
That's besides the point for a forum like this, or for a "genre" of photos like this. We survive on public opinion, and the perception of those who run the site about who's violating what. Until someone gets sued and loses, we shouldn't be surprised to see outright theft.
I support the right of the copyright holder to say "You stole my picture, you are a cretin." It is common courtesy if you know who first provided the pictures to ask whether they own the copyright and to ask for the permission of the copyright holder. If you don't do this, then you deserve to be sued -- although you probably won't be, because of the content and context.
Be excellent to each other!
S.