WASHINGTON - A collector says he believes a photograph from a private album of Civil War Gen. Ulysses S. Grant shows President Abraham Lincoln in front of the White House and could be the last image taken of him before he was assassinated in 1865.

If it is indeed Lincoln, it would be the only known photo of the 16th president in front of the executive mansion and a rare find, because only about 130 photos of him are known to exist.

Grant's 38-year-old great-great-grandson, Ulysses S. Grant VI, had seen the picture before, but didn't examine it closely until late January. A tall figure in the distance caught his eye, although the man's facial features are obscured.

He called Keya Morgan, a photography collector and Lincoln aficionado in New York, and she helped identify it as Lincoln.

Although authenticating the 2 1/2-by-3 1/2-inch photo beyond a shadow of a doubt could be difficult, several historians who saw it said the evidence supporting Mr. Morgan's claim is compelling.

Mr. Morgan asked Mr. Grant to take the photo out of the album and examining it for clues.

Mr. Grant carefully removed it and was shocked to see handwritten on the back: "Lincoln in front of the White House." Mr. Grant said he believes his great-grandfather, Jesse Grant, the general's youngest son, wrote the notation.

Also included was the date 1865, the seal of photographer Henry F. Warren, and a government tax stamp that was issued for such photos to help the Civil War effort between 1864 and 1866.

Historians say it has been decades since a newfound Lincoln image was fully authenticated. And in the Grant photo, it's not obvious to the naked eye who is standing in front of the executive mansion.

Visible are the White House, a short gate that once was near the building, and, on the lawn, a Thomas Jefferson statue that was replaced with a fountain.

Five people can be seen standing in front of the building. The tall man's face is obscured, but zooming in on the image with a computer reveals a telling beard. "Once you scan it and blow it up, you can see the whole scenario - there's a giant standing near the White House," Mr. Morgan said.

At 6-feet, 4-inches, Lincoln was the tallest U.S. president.

Mr. Morgan, who has sold photographs of Lincoln and other historical figures to the Smithsonian Institution, the White House, and others, said he purchased the image from Mr. Grant for $50,000 in February. It will be added to Mr. Morgan's $25 million collection of Lincoln artifacts and images.

Will Stapp, who was the founding curator of the National Portrait Gallery's photographs department and who now appraises fine art and photographs, said he's usually cynical about such claims. But he said he was "very satisfied that it's Lincoln" in the picture.

"It looks to me like Lincoln's physique," he said. "I can see his hairline. I can see the shadow of his beard."

White House curator William Allman said the photo appears to include Lincoln. "I guess there's always an element of doubt," he said. "It feels pretty likely, though."

Even if it's not Lincoln, it would be among the oldest photographs of the White House.

First Published March 11, 2009, 9:14 a.m.