In decipher jumbled up description type of questions, a round-about description is given in the form of certain small relationships and direct relationship between the persons concerned is to be deciphered.
Pointing to a photograph, a man said, "I have no brother or sister but that man's father is my father's son."
Whose photograph was it ?
Since the narrator has no brother, his father's son is he himself.
So, the man who is talking is the father of the man in the photograph or the man in the photograph is his son.
Hence, the answer is (b).