Some of the photos have date stamps suggesting they were taken in May 2003, which could make them the earliest evidence of possible abuse of prisoners in Iraq. The far more brutal practices photographed in Abu Ghraib prison occurred months later.

An Associated Press reporter found more than 40 of the pictures among hundreds in an album posted on a commercial photo-sharing Web site by a woman who said her husband brought them from Iraq after his tour of duty. It is unclear who took the pictures, which the Navy said it was investigating after the AP furnished copies to get comment for this story.

These and other photos found by the AP appear to show the immediate aftermath of raids on civilian homes. One man is lying on his back with a boot on his chest. A mug shot shows a man with an automatic weapon pointed at his head and a gloved thumb jabbed into his throat. In many photos, faces have been blacked out. What appears to be blood drips from the heads of some. A family huddles in a room in one photo and others show debris and upturned furniture.

"These photographs raise a number of important questions regarding the treatment of prisoners of war (PoWs) and detainees," Navy Cmdr. Jeff Bender, a spokesman for the Naval Special Warfare Command in Coronado, said in a written response to questions. "I can assure you that the matter will be thoroughly investigated."

The photos were turned over to the Naval Criminal Investigative Service, which instructed the SEAL command to determine whether they show any serious crimes, Bender said Friday. That investigation will determine the identities of the troops and what they were doing in the photos.