Pointing to a photograph of a man, Pooja said, "He is the only son of the mother-in-law of my brother's only sister." How is the man in the photograph related to Pooja?

Let's break down the statement made by Pooja step-by-step:
1. "My brother's only sister" refers to Pooja herself.
2. "Mother-in-law of my brother's only sister" means the mother-in-law of Pooja.
3. "The only son of the mother-in-law of Pooja" refers to Pooja's husband.

Therefore, the man in the photograph is Pooja's husband.