The photo, which History said was found in the National Archives by a retired federal agent named Les Kinney, appears to show a tall, trousers-wearing, short-haired woman seated on a dock in Jaluit, an atoll in the Marshall Islands, with her back to the camera.
It also appears to show Mr. Noonan and maybe even the Electra itself, on a barge off in the distance.
Shawn Henry, a former F.B.I. executive assistant director who has been working with History to investigate the photo for about a year, said facial identification experts called it likely that the photos showed Ms. Earhart and Mr. Noonan.
He said the Marshall Islands theory is supported by other evidence, too: pieces of metal that were found in the area and could have come from the Electra; an interview Mr. Henry conducted with an islander who claims to have seen Ms. Earhart around the time of her disappearance; and government records citing reports about Ms. Earhart being imprisoned by the Japanese, though the reports mentioned have not been found.
“When you take it all together, to me, it’s beyond a reasonable doubt. That photograph is just a bow on top of a box of evidence,” Mr. Henry said in a phone interview. “And that bow, to me, just ties it all together.”
He sounded confident — just as confident, in fact, as Ric Gillespie, who may be the best-known proponent of another, entirely different theory.
Mr. Gillespie is the executive director of The International Group for Historic Aircraft Recovery, a nonprofit that has spent decades searching for Ms. Earhart. He thinks the aviator landed her plane on an atoll (then called Gardner Island, now Nikumaroro) that is more than a thousand miles away from the Marshall Islands.
This week, researchers from that organization are on their 12th mission to Nikumaroro in search of the aviator’s remains. That voyage is the one being supported, in part, by National Geographic and four dogs.
The organization’s previous missions have found promising artifacts, like pieces of what could be airplane metal and parts of jars manufactured by American companies during the 1930s — including one used for a freckle ointment for women, which wouldn’t have been out of place among the possessions of the freckled female aviator.
“There is such a public desire for an answer to this mystery,” Mr. Gillespie said. “Because it is such a complex and multidisciplinary effort to investigate it, I see it as a wonderful opportunity to explore and demonstrate and teach how we go about figuring out what is true.”
The Marshall Islands and Nikumaroro theories are at odds not only with each other, but with the U.S. government’s official version of events: that Ms. Earhart plunged straight into the ocean in a failed attempt to reach a scheduled stopover at Howland Island.
That position is supported by Dorothy Cochrane, a curator in the aeronautics department at the Smithsonian National Air and Space Museum.
The Japanese capture theory has historically been tough to swallow because radio calls suggested that Ms. Earhart was near Howland Island — which is hundreds of miles southeast of Jaluit — and running low on fuel before she disappeared, Ms. Cochrane said.
“She says she is getting low on fuel, then calls 45 minutes later with a worried tone saying she is running the line on which she hoped to cross over Howland Island,” Ms. Cochrane said. “But she doesn’t. She doesn’t say she’s departing the area, nor does she call Mayday.”
Mr. Henry said that while the crash-and-sink theory holds weight in the popular imagination, “there’s not one shred of evidence that she crashed into the ocean.” Millions of dollars have been spent to explore ocean floor around Howland Island, and no airplane has turned up yet.
“We all grew up with the story. I grew up with the story since I’ve been a small kid, that this is what happened to her,” he said. “So it’s hard, I think, for people to accept that it didn’t.” He hopes that the Marshall Islands theory will not only be proven beyond the shadow of a doubt, but that researchers will one day unravel the story of Ms. Earhart’s final days behind bars.
Of course, he might be wrong about everything. And that could mean no end in sight for a search that has spanned decades and cost millions, led by enthusiasts who refuse to believe that their country’s most famous female aviator could have disappeared without a trace.