TMZ has posted a picture of a kid who appears to be JUSTIN BIEBER playing BEER PONG.  (--Check it out here.)

--A source says this game took place in either Canada or Georgia.  But it was last year, when Justin was 17 . . . so even if it was in Canada, he would have been too young to drink alcohol . . . which the source says he DID.

--Another source says the game went down in Alabama in June.