When does the wife of a missing person begin her waiting period ('iddah) after his death is confirmed without finding his body?

The death of your sister's husband cannot be confirmed by mere pictures, as they can be manipulated. The original presumption is that he is alive, and the marital bond remains. His wife should not observe the 'iddah (waiting period) until the matter is brought before a Sharia judge to rule on the case according to Islamic legal provisions concerning the wife of a missing person.