Inscribed "With love from Kate and George, 17/11/15" it was one of those faded, formal, sepia wedding pictures. Husband standing apprehensively but proudly in his First Australian Imperial Force uniform with the shiniest of boots. Wife slightly less so in her neck-to-ankle wedding dress with her new, probably too-tight shoes, poking out from under the lace hem.

It was a studio photograph of Albert George Searle and Kate McLeod, but it could have been almost any couple. A moment caught in a soldier's life just before he was sent off to who-knows-where. A new wife thinking about how she'd cope with her man away. A keepsake. A constant reminder for loved ones left at home. For the National Library of Australia, nothing could have better illustrated the message for its new exhibition, Keepsakes: Australians and the Great War.

Although the exhibition is staged to mark the centenary of World War I, it is not just an exhibition about war, says the library's director of exhibitions Guy Hansen. Instead, it's about how we remember the war.

"There's no-one left who was there who can tell us what they saw," he says.

"So this exhibition is all about their keepsakes. The photos they sent home to their families. The diaries they kept day-to-day. Their stories, their medals and their ephemera. These are the things we now have to help us understand the war."

Assistant Curator Felicity Harmey says the minute she saw the image of George and Kate Searle, she knew it told "the story we wanted to tell".

"For us, this exhibition is about collecting people's lives - through their keepsakes," she said.

"I was just poking around the picture stacks and saw this image. It really was an accident. It was in a drawer labelled 'uncatalogued'. It was the sort of keepsake you could imagine being on almost every Australian mantelpiece in every Australian home in 1915."

When you look at the picture you can't but wonder what they were thinking. How long would he be away? What would happen to him? Would he come home?

For Curator Susannah Helman, this "accidental" find was exactly what she was looking for. "We were looking for an image that shouted Keepsakes," she says.

"For every exhibition you work on, you look for an object, something that will carry the thesis of the exhibition. This was it."

The image remained a mystery until the curatorial team, led by Dr Hansen, removed the base board of the photograph and found the dedication. From there Dr Helman trawled through service records at the National Archives of Australia for the name George Searle. She married that research with the Library's own Trove service and, by linking his marriage date on his service records with other records, she had him.

"It was a challenge … it's always an exciting challenge to solve a mystery. It's really what research is all about and what I love about this job."

Finding out if George and Kate had any descendants was a lot easier. Dr Helman checked the Coonamble phone book, the last known home of the family, and rang the first Searle she found. It was answered by George and Kate's great-granddaughter, Connie Searle.

The last piece of the puzzle was, according to the curators, the best. They were directed to family matriarch Barbra Searle, 87, of Mudgee. She married one of the couple's four sons, Colin Searle, and lived with George and Kate for 15 months.

Mrs Searle said she couldn't believe it when the Library contacted her about the image. "Who knew that picture would turn up in the National Library?

"Back in those days just about every family from these small towns had someone at the war. You just have to look at the number of names on the local war memorials to see how many men we lost.

"I think many people wanted to join up then because so many had been born in England. Maybe it was a way to prove we'd grown up."

So what were George and Kate like? "I remember George met Kate in Randwick," Mrs Searle says. "Her family, the McLeods, were well known there, but I don't know exactly how they came to meet. I think her family also had land around Cowra way."

Official records tell us George enlisted in the Australian Army in September 1915 and three months later left for Egypt in the troop ship Kanowna. In between, he married his Kate.

He didn't fight in any significant battles. He didn't win any medals, but - with 400,000 other Australians - he enlisted to serve his country, and did whatever it asked of him.

Afterwards he did come home to Kate, and worked as a shire clerk in Coonamble.

"George and Kate were a sound couple," Mrs Searle said. "These days it's hard to imagine how they must have coped with four sons overseas in wartime. One didn't come back. Fred. He is buried at Ypres.

"Kate was a very strong woman. I suppose she had to be then. But they had a happy marriage. George was a fantastic man. Very easy-going, soft sort of man. Everyone liked him.

"Funny thing though, I don't remember anyone ever calling Kate by her Christian name. She was always Mrs Searle. But she was a very community-spirited woman. She was very active in the Red Cross and CWA, while George worked very hard for Legacy."

In their way, she said, they had a successful life together.

Like all good mysteries, sometimes there's one thing still to uncover. How did the National Library acquire the image? Acquisition records show only that it was given to the NLA by a J. C. Bryant. Mrs Searle doesn't know anyone of that name.

"It is one of life's mysteries," she said. "But I would really like to find out who this J. C. Bryant was."

So would the National Library. But that's another story.

Sally Hopman, a former journalist, works at the National Library of Australia.

Keepsakes: Australians and the Great War is on at the National Library of Australia, Canberra, from November 26, 2014 untilJuly 19, 2015. Free exhibition. nla.gov.au/exhibitions/keepsakes