SAN DIEGO >> The photo shows a decorated Navy SEAL holding up the head of a dead Islamic State fighter by the hair while clenching a knife in his other hand.

It will be up to a seven-man jury of mostly combat veterans to decide if it was a snapshot in poor taste of an enemy who succumbed to battle wounds or a trophy shot of a war prisoner killed under his care.

The court martial of Special Operations Chief Edward Gallagher began today with the defense claiming he had done nothing more than provide medical care to the militant wounded in an air strike and the prosecutor accusing the war veteran of premeditated murder.

Defense attorney Tim Parlatore told jurors in opening statements that there’s no body, autopsy or forensic evidence to show a killing happened. He said the case was built on lies by junior SEALs who hated Gallagher because he was tough.

“This case is not about murder,” Parlatore said. “It’s about mutiny. He didn’t murder or attempt to murder anyone.”

The prosecutor showed a photo of Gallagher posing with the corpse along with other images of the bandaged curly haired adolescent.

Gallagher texted one photo to friends with the message: “Good story behind this, got him with my hunting knife.”

“He celebrated that stabbing, he celebrated that murder,” the prosecutor, Lt. Brian John told jurors.

Parlatore has said the text was an attempt at dark humor.

Gallagher, whose case has drawn President Donald Trump’s attention, faces seven counts that include premeditated murder and attempted murder. He’s also accused of shooting two civilians — an elderly man and a school-age girl — from sniper perches in Iraq in 2017. He has pleaded not guilty and could face a life sentence.

The trial, which is expected to last up to three weeks, is exposing fractures in the secrecy that typically shrouds the elite special forces as fellow troops testify against Gallagher, who had served eight tours of duty and earned two Bronze Stars for valor.

Three SEALS were scheduled to testify for the prosecution Wednesday.

Today, Lt. Thomas MacNeil, who roomed with Gallagher, testified that their SEAL team provided support to Iraqi forces clearing an area outside Mosul when he heard a radio transmission on May 3, 2017, that an airstrike had wounded an Islamic State fighter.

“I heard Chief Gallagher announce, ‘Lay off, he’s mine,’” MacNeil said.

Gallagher initially began treating the teen militant’s wounds, which was caught on video the jury will see. The question is what happened after the footage stopped.

John said the wounded prisoner was in stable condition after treatment.

After another SEAL left his side, Gallagher pulled a knife from his medical bag and repeatedly stabbed the boy in the neck, John said. Another SEAL saw the assault and said blood was pouring out of the teen.

Parlatore said the militant died of his injuries from the airstrike and noted that Iraqi forces had been with him two hours before Gallagher became the first to treat him. He also said no blood was found on the knife.

After the boy died, Gallagher had his re-enlistment ceremony conducted with the body and posed with fellow troops for photos.

MacNeil, who posed with them, testified that the photos were inappropriate because he was taught to not disgrace casualties on the battlefield.

The defense does not dispute that Gallagher posed with the corpse.

“Was the photo in poor taste? Probably,” Parlatore told jurors in his opening statement. “Was the photo evidence of murder? No.”

The jury is composed of five enlisted men, including a Navy SEAL and four Marines, plus a Navy commander and a Marine chief warrant officer. Most of the jurors have served in conflicts in Iraq and Afghanistan.

Gallagher’s defense has been championed by his family and some congressional Republicans who have claimed that he’s a hero getting railroaded. Trump intervened to get Gallagher removed from the brig as he awaited trial and is said to be considering a pardon for him.

Gallagher’s accusers are cowards who wanted to derail his nomination for a Silver Star for valor and a promotion to teach urban warfare, Parlatore said.

After returning to San Diego from their deployment, MacNeil said he got a text to stay after work one day for a meeting in the parking lot, where Gallagher rushed at him, grabbed his face and said, “You take me down, I’ll take all you down.”