The flag that is being used for the background is the flag that was flying above Fort McHenry.
The Flag was flown over the fort when 5,000 British soldiers and a fleet of 19 ships attacked Baltimore on September 12, 1814. The bombardment turned to Fort McHenry on the evening of September 13, and continuous shelling occurred for 25 hours under heavy rain. When the British ships were unable to pass the fort and penetrate the harbor, the attack was ended, and on the morning of September 14, when the battered flag still flew above the ramparts, it was clear that Fort McHenry remained in American hands. This revelation was famously captured in poetry by Key, an American lawyer and amateur poet. Being held by the British on a truce ship in the Patapsco River, Key observed the battle from afar. When he saw the Garrison Flag still flying at dawn of the morning of the 14th, he composed a poem he originally titled Defiance of Ft. McHenry (though some accounts hold Defense of Fort McHenry). The poem would be put to the music of a common tune, retitled The Star-Spangled Banner, and a portion of it would later be adopted as the United States National Anthem. Since its arrival at the Smithsonian, the flag has undergone multiple preservation efforts.