Concept:
Such reasoning problems require interpreting family relationships logically.
Step 1: Analyze the statement.
The man says he has no brother or sister.
Thus, “my father's son” must refer to the man himself.
Step 2: Interpret the sentence.
The statement becomes:
\[
\text{That man's father is me.}
\]
Step 3: Conclusion.
If the man in the photograph has the speaker as his father, then the photograph must be of his son.