Pointing to a photograph, a man said, "I have no brother or sister but that…

Concept: In blood-relation puzzles, a self-referential phrase like "my father's son" collapses to one specific person once the sibling count is known — if the speaker has no brothers or sisters, "my father's son" can only be the speaker himself, since no other son of that father exists.

Application:

1. The statement gives one equation: "that man's father is my father's son."

2. Since the speaker has no siblings, "my father's son" = the speaker himself.

3. Substituting: "that man's father is the speaker."

4. So the speaker is the father of the man in the photograph, which makes the man in the photograph the speaker's son.

Cross-check against the other options:

• If the photograph were of the speaker himself, the statement would need to equate the speaker's own father directly with the man in the photo — it instead equates the man's father with the speaker.

• If the man in the photo were the speaker's father, then "that man's father" would be the speaker's grandfather, not the speaker — contradicting the given equation.

• If the man in the photo were the speaker's grandfather, the deduction would require two father-links from the speaker, but the statement supplies only one substitution.

Therefore, the photograph was of the speaker's own son.