Originally posted by malinga
I'm tempted to say picture is himself (partygoer not host) but I think it's partygoer's 1st cousin instead.
Host's father's only niece would have host's fathers wife as only aunt.
So hosts fathers wife has a only brother who has ...[text shortened]... esence which would be another aunt so picture is impossible...
The father has one and only one niece. That doesn't give much information.
However, the niece only has one aunt. This aunt could be the father's only sister, or the father may have no sister, and it's the niece's mother's only sister.
This aunt has only one brother. That brother is either the father or the niece's mother's only brother.
The only son of the brother is either the person showing the picture, or the niece's maternal cousin.
The puzzle is only interesting if it's the person showing the picture, so that's who it is.
Oh right, the wife of the husband would be an aunt (thanks malinga) - this puzzle isn't well constructed I think. What if the mother of the host didn't marry the father? Then she's not the niece's aunt right?