riddle

his son
He's looking at a picture of his son.

He is looking at himself.

nope carditel, it's son.

If you look at your picture, you can't say "my father is my father's son"

Au contraire - if that's your son picture "his father /you/ is my father's son".

The man in the picture is his fathers son , namely himself.

He says, "That man's father is my father's son." In other words, he is saying, "That man's father is me." Therefore, he is looking at a picture of his son.

The answer could be either , if the person looking at the photo is female it can only be son but if the person looking is male it could be either, son or self.

No, it couldn't.

I think both Debra and I explaned it pretty well.

And I also think it's pretty clear itself - once more: "That man's father is my father's son".
Talk to yourself - look at your picture and try to tell that yourself. Can you look at yourself and say "my father is my father's son"?
I don't think so. Not even on Jerry Springer.

If you look at your son's picture though, you CAN say "his father is my father's son".

And females and males have nothing to do with it. And there is absolutely no chance that both answers are correct.