A National Park Service volunteer browsing on eBay has made an astonishing discovery: a long-lost photo that park officials have described as a "priceless" piece of Civil War history. The stereo view image depicts Selina Gray (at right, above), an enslaved woman who was head housekeeper at the Virginia home of Confederate General Robert E. Lee. NPS spokesman Lee Werst described Gray as a "pivotal but little-known figure in our nation's history." Her bravery in defending the house after Gen. Lee's family left helped to save cherished heirlooms that had once belonged to President George Washington.

The Park Service bought the photo for $700 from an eBay seller in England who had found it in a box of unwanted photographs at a junk sale. NPS volunteer Dean DeRosa credited "sheer luck" for his discovery of the photo on the website. "I recognized Selina Gray instantly," he told NBC News.

The photo of Selina Gray is displayed at the spot where it was taken on the Arlington House estate. An inscription on the back reads "Gen Lees Slaves Arlington Va." Jose Luis Magana / AP

- Joe Bohannon and David Arnott