The Man in The Photograph

A man is looking at a photograph of someone. His friend asks who it is.

The man replies, 'Brothers and sisters, I have none. But that man's father is my father's son'.
 
Who is in the photograph?

Know here the relationship between! 

Source 

Relation With The Man in Photograph

What was the incident? 

The person in photograph is the man's son. Since the man doesn't have any 

brothers or sisters, the statement my father's son is himself. A shortened 

version would be this man's father is myself; so he is the father of the man in

the picture.