White House photographer Pete Souza took this photo of President-elect Barack Obama moments before Obama took the oath of office. 

(Photo by Pete Souza/The White House)

President Obama and first lady Michelle Obama shared a moment at the Inaugural Ball on January 20, 2009.

(Photo by Pete Souza/The White House)

The next day, Obama entered the Oval Office to begin his first full day as America's 44th president.

(Photo by Pete Souza/The White House)

LONDON, ENGLAND - APRIL 22: In this handout provided by The White House, President Barack Obama, Prince William, Duke of Cambridge and First Lady Michelle Obama talks with Prince George at Kensington Palace on April 22, 2016 in London, England. The President and his wife are currently on a brief visit to the UK where they attended lunch with HM Queen Elizabeth II at Windsor Castle and later dinner with Prince William and his wife Catherine, Duchess of Cambridge at Kensington Palace. Mr Obama visited 10 Downing Street this afternoon and held a joint press conference with British Prime Minister David Cameron where he stated his case for the UK to remain inside the European Union.

(Photo by Pete Souza/The White House via Getty Images)

Obama reads a letter that former President George W. Bush left for him in the Oval Office's resolute desk. Leaving a letter for the incoming president has become a White House tradition.

(Photo by Pete Souza/The White House)

Obama toured the White House grounds with curator William Allman, chief usher Adm. Stephen Rochon, and presidential personal aide Reggie Love. 

(Photo by Pete Souza/The White House)

Here's a photo of Obama meeting with senior advisers in the Oval Office during the third week of his presidency.

(Photo by Pete Souza/The White House)

Wearing an embroidered crew jacket, Obama waited for the first of many flights aboard Air Force One.

(Photo by Pete Souza/The White House)

Obama gave his first State of the Union address on February 24, 2009.

(Photo by Pete Souza/The White House)

The Obamas walked to Marine One on the South Lawn before heading off on one of their first trips to Camp David.

(Photo by Pete Souza/The White House)

In this handout from the White House, U.S. President Barack Obama works on his Newtown speech at The Music Center at Strathmore auditorium on December 16, 2012 in Bethesda, Maryland. Obama later visited Newtown, Connecticut to speak at an interfaith vigil for the shooting victims from Sandy Hook Elementary School.

(Photo by Pete Souza/The White House via Getty Images)

The Obamas were welcomed by Queen Elizabeth II to Buckingham Palace in London while in town for the G20 summit. 

(Photo by Pete Souza/The White House)

Obama gave a fist bump to a US soldier while visiting troops at Camp Victory in Iraq on April 7, 2009.

(Photo by Pete Souza/The White House)

President Obama and Michelle smiled at each other inside a White House elevator after a Cinco de Mayo celebration.

 (Photo by Pete Souza/The White House)

Obama and Vice President Joe Biden practiced their putting skills on the White House green.

(Photo by Pete Souza/The White House)

Obama tours the Pyramids of Giza in Egypt for the first time during his 11th presidential trip abroad.

(Photo by Pete Souza/The White House)

In this July 2009 photo, Obama attended his first G8 summit, which was held in L'Aquila, Italy.

(Photo by Pete Souza/The White House)

Over the summer of 2009, Obama visited the Grand Canyon in Arizona.

(Photo by Pete Souza/The White House)

Obama laughed at a picture of himself during an interview on the "Late Show with David Letterman."

(Photo by Pete Souza/The White House)

The Obamas welcomed children from local schools for Halloween festivities at the White House.

(Photo by Pete Souza/The White House)

The Obamas posed for their first holiday portrait in front of the official White House Christmas tree.

(Photo by Pete Souza/The White House)

At the beginning of the new year, White House photographer Pete Souza took this photo of Obama meeting with members of his cabinet. The president's chair is marked with a plaque engraved with his inauguration date.

(Photo by Pete Souza/The White House)

The Obamas danced during the Governors' Ball held in the East Room of the White House.

(Photo by Pete Souza/The White House)

Obama reads some documents while waiting for Marine One at the Westchester County Airport in New York.

(Photo by Pete Souza/The White House)

Obama speaks with a congressman about the healthcare-reform bill. "In those final days before the vote, the President made hundreds of calls," wrote White House photographer Pete Souza.

(Photo by Pete Souza/The White House)

Alongside White House staff and Vice President Joe Biden, Obama clapped while watching the historic House vote to pass the Affordable Care Act.

(Photo by Pete Souza/The White House)

Obama boarded Air Force One while the sun set at Miami International Airport. 

(Photo by Pete Souza/The White House)

The Obamas pretended to sing with an a capella group after a holiday tour of the White House.

(Photo by Pete Souza/The White House)

"A lighter moment during a meeting in the Situation Room of the White House," Souza wrote.

(Photo by Pete Souza/The White House)

Obama shook hands with US soldiers at Bagram Airfield after an all-night, unannounced flight to Afghanistan in December 2010.

(Photo by Pete Souza/The White House)

The Obamas stared at Rio de Janeiro's famous Christ the Redeemer statue while visiting Brazil in March 2011.

(Photo by Pete Souza/The White House)

Obama saluted a Marine while walking toward Marine One helicopter on the South Lawn of the White House.

 (Photo by Pete Souza/The White House)

Taken on May 1, 2011, from the White House Situation Room, Obama's national-security team monitored the real-time mission against Osama bin Laden. Souza took approximately 100 photographs during this confidential meeting.

(Photo by Pete Souza/The White House)

"The president was ready to announce the news about the mission against Osama bin Laden and was putting the finishing touches on his statement in the Outer Oval Office. As he did so, the networks broke in with bulletins confirming that bin Laden had been killed and a photograph of him appeared on the television screen in the background near the Vice President and Press Secretary Jay Carney," Souza wrote.

(Photo by Pete Souza/The White House)

"One of the most memorable moments of the year was when the president hugged Rep. Gabrielle Giffords as he walked onto the floor of the House Chamber at the US Capitol to deliver his annual State of the Union address," Souza wrote in January 2012. Giffords was shot in a 2011 mass shooting in Arizona.

(Photo by Pete Souza/The White House)

"The President hugs the first lady after she had introduced him at a campaign event in Davenport, Iowa. The campaign tweeted a similar photo from the campaign photographer on election night and a lot of people thought it was taken on election day," Souza wrote. When the campaign tweeted it on election night, it became the most retweeted photo of all time.

(Photo by Pete Souza/The White House)

Obama kissed the first lady for the "kiss cam" during the US men's Olympic basketball team's game against Brazil in Washington, D.C.

 (Photo by Pete Souza/The White House)

Obama sang "Happy Birthday" to Michelle in the Blue Room of the White House in 2013. Her new hairstyle attracted a lot of attention.

(Photo by Pete Souza/The White House)

In this photo, Obama sits in front of cameras taking images that will later make a 3D portrait for the Smithsonian Institution.

(Photo by Pete Souza/The White House)

"We were at the NATO Summit in Wales when someone mentioned to the President that Stonehenge wasn't that far away. 'Let's go,' he said. So when the Summit ended, we took a slight detour on the way back to Air Force One," Souza wrote in September 2014.

(Photo by Pete Souza/The White House)

Obama laughed as he and Michelle recorded a holiday video message in the Map Room of the White House.

(Photo by Pete Souza/The White House)

This March 2015 photo shows Obama delivering remarks during an event to commemorate the 50th Anniversary of Bloody Sunday and the Selma to Montgomery civil-rights marches. 

(Photo by Pete Souza/The White House)

Obama shook hands with President Raúl Castro of Cuba during the Summit of the Americas on April 11, 2015. The US and Cuba have moved toward a historic thaw in relations over the past year. 

(Photo by Pete Souza/The White House)

U.S. President Barack Obama and his daughters Malia (L) and Sasha, watch on television as first lady Michelle Obama takes the stage to deliver her speech at the Democratic National Convention, in the Treaty Room of the White House in Washington September 4, 2012.

(REUTERS/White House/Pete Souza/Handout)