WASHINGTON — It may prove to be the defining image of Barack Obama’s presidency.

Sunday, May 1, 2011. Obama is huddled with his national security team in the White House Situation Room, receiving real-time updates on the mission to kill or capture the most wanted man in the world: Osama bin Laden.

Obama, wearing a white collar shirt and black jacket with no tie, sits in a small chair in a corner of the room, flanked by Vice President Joe Biden and Joint Chiefs of Staff Chairman Adm. Mike Mullen.

The president, so often pictured in a relaxed pose with a smile on his face, has a grave expression. He is steely-eyed and hunched forward. He is staring straight ahead at a screen not visible in the photo.

Across the table, Secretary of State Hillary Clinton appears worried. She is also staring ahead, one hand over her mouth and another over a classified document in her lap. Secretary of Defense Robert Gates is seated to her left.

White House Chief of Staff Bill Daley and presidential homeland security and counterterrorism adviser John Brennan are among a small group standing in the back.

A partially obstructed presidential seal hangs behind Obama.

“It was probably one of the most anxiety-filled periods of time, I think, in the lives of the people who were assembled” there, Brennan told reporters Monday. “It was clearly very tense, a lot of people holding their breath. And there was a fair degree of silence as it progressed, as we would get the updates.”

Brennan described “a tremendous sigh of relief” when the news came that bin Laden had finally been found, ending nearly a decade of painstaking work and frustration.

Obama’s advisers disagreed over whether to launch the risky operation. “It was one of the most gutsiest calls of any president in recent memory,” Brennan said.

The photo, taken by current White House photographer Pete Souza, captured “a defining moment in history very well,” said Eric Draper, a photographer for President George W. Bush.

It’s “very dramatic” and a “study of the intensity” of the time, he said.

“There are some moments that the photographer really just has to be there,” he said. “The moment is so powerful” that it speaks for itself.

Over the years, a series of photos have come to define the presidency in the public mind.

There is a smiling Harry Truman after his upset win over Gov. Tom Dewey in the 1948 election, holding up a copy of the Chicago Daily Tribune with the mistaken banner headline “Dewey Defeats Truman.”

Shortly after taking office in 1961, John F. Kennedy was photographed in the Oval Office, silhouetted by the light of the office’s center window. The president, his back to the camera, is leaning over a table behind his desk, seemingly with the entire weight of the Cold War world on his shoulders.

There is also JFK’s successor, Lyndon Johnson, on Nov. 22, 1963, taking the oath of office on Air Force One as a grief-stricken Jacqueline Kennedy stands by his side.

Nearly five years later, on July 31 1968, Johnson was photographed in the White House Cabinet Room, slouched over the conference table with his head resting on his fist while listening to a tape sent from Vietnam by his son-in-law, Marine Capt. Charles Robb. Johnson appears a near-broken man — a reflection of a presidency all but wrecked by the Vietnam War.

There is the image of Richard Nixon on Aug. 9, 1974, flashing the triumphant “V for Victory” sign before boarding a helicopter to leave the White House after submitting his resignation.

On Inauguration Day 1981, a beaming Ronald Reagan was photographed next to his wife Nancy, standing up through the open roof of his presidential limousine with his hands clasped together over his head in triumph.

Twenty years later, shortly after the 9/11 attacks, President George W. Bush was seen by the world standing atop a pile of rubble at Ground Zero. The president, surrounded by New York City firefighters and speaking through a bullhorn, promised that the terrorists “will hear from all of us soon.”

That moment — witnessed by Draper — proved to be the peak of Bush’s popularity. “I got a chill when [it] happened,” he recalled.

Obama’s presidency is all but certain to go through countless twists and turns before he finally leaves office. But the image of him hunkered down on Sunday — trying to bring an end to a long chapter in America’s struggle against terrorism — may be one of the few that breaks through the clutter of the modern media culture and leaves an enduring mark.

Only time will tell.