A security team swept the area and investigated the problem after a bag being screened was red-flagged at about 1:15 p.m. A screener reported seeing a "suspicious" image while X-raying carry-on luggage, the Atlanta Journal Constitution reported.
Checkpoints reopened around 4 p.m. and operations were returning to normal, the newspaper said, but some flights were delayed and long lines of delayed travelers still jammed the main terminal.
Airport and federal security officials said they found no dangerous items and took no one into custody. The newspaper said it wasn't clear later in the day that any single piece of luggage was linked to the alert.
"If it was a glitch, we will find out," Willie Williams, the federal security chief for Hartsfield-Jackson, said at a news conference.
He said security camera pictures and the image seen by the screener were being analyzed.
Gal Gadot cast as Wonder Woman for 'Batman vs. Superman'
Exploding whale video goes viral on Internet