ROCHESTER, N.Y. — Seated by a window in the Illinois state Capitol in 1860, a beardless, bow-tied Abraham Lincoln held still for 25 seconds for what would become a classic campaign portrait of the soon-to-be president. It was undoubtedly a personal favorite.

“That looks better and expresses me better than any I have ever seen,” Lincoln, who had recently launched his run for the White House as the Republican nominee, said in a letter to photographer Alexander Hesler. “If it pleases the people, I am satisfied.”

Twenty years later, images of the slain Civil War leader were in high demand. Hesler’s wet-plate collodion negative was used to create a high-definition, silver-gelatin interpositive — a new-technology format from which several thousand prints were generated and sold in the late 19th century.

Leap forward to 1933: During shipment by parcel post to St. Louis, the original glass plate is accidentally broken and ends up as a shattered artifact in the Smithsonian Institution’s vault. But the 8-by-10-inch clone — evidently in the same package and similarly damaged — disappears.

To mark the 200th anniversary of Lincoln’s birth Thursday, the long lost positive transparency goes on display, beginning today, at the George Eastman House museum of photos and film.

It was sent there for repair in December 2006 by a Midwestern collector of Lincoln materials who didn’t realize he owned what curators regard as a national treasure. He has declined to be identified.

“This is the closest you will ever get to seeing Lincoln, short of putting your eyeballs on the man himself,” said Grant Romer, an expert on Lincoln images and the museum’s director of photograph conservation.

Next to the best-preserved paper prints, the three-quarter profile — shot with the aid of a head rest on a quiet Sunday in Springfield, Ill., on June 3, 1860 — is striking in its clarity and tonal range.

Visible in the backlit glass plate is every wrinkle and freckle on Lincoln’s lopsided face, the irregular curve of his thick lower lip, unruly hairs in his bushy eyebrows, a mole on the right cheek. “It’s almost more than you want to see,” Romer said, laughing.

With its dermatological detail, the picture becomes a vital authentication reference.

Lincoln was the first U.S. president to be extensively photographed — more than 125 highly collectible portraits of him survive.

Though not as well-known as other Lincoln photos — “from a tousle-haired, Byron-esque pose” captured by Hesler in 1857 to the bearded and “sometimes absolutely haggard” views of Lincoln as president — the official campaign picture looks formal and dignified but also more handsome and fresh-faced, Romer said. “It’s the most noble portrait of him, very heroic,” Romer said.