But zoom in closer, really close, and a startling image takes shape at the center of the crowd. A tall, slim figure astride a horse. A familiar profile. That signature stovepipe hat, a white gloved hand raised in salute.

Could it be President Abraham Lincoln shortly before delivering his Gettysburg Address?

Some Civil War scholars and experts in early photography believe it is.

It is one of two three-dimensional images taken, experts say, within minutes of each other as Lincoln arrived Nov. 19, 1863, to dedicate the cemetery just four months after the bloody battle. If it is Lincoln, the photograph holds enormous historical importance and adds two invaluable images to the slim archive of Lincoln photographs.

"This find doubles the number of apparent images of Lincoln at his greatest moment," said Bob Zeller, president of the Center for Civil War Photography, who explained that only two other images of Lincoln at Gettysburg were known to exist. "When I saw it for the first time, my jaw dropped."

The latest discovery - unveiled formally at the annual conference of the Lincoln Forum yesterday - was hiding in plain sight.

The photos were among the more than 5,000 Civil War images included in the Library of Congress archive. Librarians began scanning the archive in 2000 and made them available to the public online.

Amateur historian and author John Richter of Hanover downloaded a large 3-D image from the archive several years ago. But it wasn't until last year, after a computer upgrade, that he was able to magnify the photos enough to pick out a figure deep in the crowd.

"It's that much more convincing in 3-D," said Richter, who has spent hundreds of hours studying images from the period and is a board member of the Center for Civil War Photography.

These 3-D images, or stereoviews, brought to life the leading figures of the day and delivered the horrors of the war to millions.

Among the details that came into focus with high magnification was a mounted figure, his gloved hand lifted to his forehead.

"Who else would salute the troops but the commander-in-chief?" Richter said.

He said some critics questioned why Lincoln would salute with his left hand. "Perhaps he was holding the reins with his right hand," he said.

Naysayers have emerged, but that doesn't bother Richter or Zeller.

"There's going to be debate," Zeller said, "but I believe we've found it."