The photograph shows U.S. Marine Lance Cpl. Ted Boudreaux Jr. standing next to two Iraqi boys, the Washington-based Council on American-Islamic Relations said. One of the boys holds a cardboard sign that reads "Cpl. Boudreaux killed my Dad, (then) he knocked up my sister!"
The photo has been circulating around the Internet for at least a month.
"We're asking was it legitimate, what were the circumstances ... or was it a joke?" said council spokesman Ibrahim Hooper.
Boudreaux is a reservist with Headquarters and Service Company, 3rd Battalion, 23rd Marines. The New Orleans-based infantry unit deployed to the Kut area of Iraq in May and returned home in mid-September.
Marine Corps spokesmen said an investigation is under way, but its results may not be released for another week or two.