For decades, a photo album that helped convict Nazi generals of war crimes was kept in a cupboard in suburban Australia.

The photos of the Mauthausen concentration camp in Austria were meant to be propaganda, but one copy, smuggled out of the camp by Spanish anti-fascists, was used as evidence at the Nuremberg trials after the war.

That album has been donated to a museum in Sydney, but the story of how it ended up in Australia remains mysterious.

Annabelle Ciufo was in her early teens the first time she saw the historical artefact, though she didn't understand its significance then.

It came to Australia in 1973 with her aunt, Ana Ivanovic, a Yugoslavian woman who survived World War II.

When Ms Ivanovic landed in Australia, she was exhausted but bursting with excitement — she had not seen her sister, Ms Ciufo's mother, for over 20 years.

"Out of the suitcase came chocolates and gifts from Yugoslavia, old doilies and tablecloths," Ms Ciufo remembers.

The last thing to be pulled from the suitcase was a mysterious photo album showing the Austrian World War II concentration camp, Mauthausen.

Images of suffering and cruelty at Mauthausen

The album began with images of stone buildings, Austrian countryside, visiting dignitaries and Nazis in uniform.

As it progressed, the photos became more disturbing.

They showed images of dead bodies piled up, children in freezing conditions behind barbed wire, a man, dead in the snow wearing only a thin camp uniform with no shoes.

Annabelle Ciufo decided to donate the album to the Sydney Jewish Museum. ( Supplied: Annabelle Ciufo )

The album had belonged to Ms Ciufo's uncle, Bogden Ivanovic, who was a political prisoner at Mauthausen.

Ms Ciufo never met him, as he died in the early 1970s in Yugoslavia.

As an adolescent, Ms Ciufo was unsure how to respond to what she saw.

"These pictures revealed such suffering and cruelty, beyond what I could know or even understand," says Ms Ciufo.

The family didn't know the remarkable story of how the images made it out of the camp, nor how Mr Ivanovic came to own them.

From a flour sack to a climate-controlled museum

Ana Ivanovic, Ms Ciufo's aunt, didn't want to keep the gruesome album her husband had left behind, so it stayed in a calico flour sack inside a cupboard in a family member's NSW home.

"Every now and then I'd ask if I could have a look, but then we forgot about it for many years," Ms Ciufo says.

After a death in the family, the album in the flour sack moved to another family member's house, kept again in the back of a cupboard for many years.

In 2018, after yet another family death, Ms Ciufo unearthed the album and decided it was time to donate it to a museum.

Roslyn Sugarman, the head curator at the Sydney Jewish Museum, says as soon as she opened the album's cover she could tell it was a significant historical artefact.

The album contains Bogden Ivanovic's identification number from the Mauthausen camp. ( ABC RN: Alice Moldovan )

On the inside cover of the album, Mr Ivanovic had pasted the registration badge that he received at Mauthausen, labelled with an inverted, red triangle with a "J" in the middle.

"The 'J' doesn't refer to 'Jewish', however. It denotes the former Yugoslavia, in the German spelling. The red triangle shows that he was a political prisoner," Ms Sugarman explains.

"There's no name, he was only identified by a number, 13575. [He included this] almost as a symbol of saying: 'This is me, I was there, I lived through this.'"

The political prisoners' dangerous mission

The photo album is a remarkable testimony to the bravery of a handful of cunning prisoners who worked in the camp's photographic lab.

The Nazis had directed prisoners to make five copies of the album, to send to various generals so they could be used to oil the Nazi propaganda machine.

A sixth, clandestine copy was made by the prisoners and smuggled out of the camp.

"Those involved were Spanish prisoners of war and they clearly had an agenda," Ms Sugarman says.

"They were anti-fascists and they wanted to resist in any way they could. They smuggled out negatives and copies at great risk to themselves."

The images were used as evidence in the Nuremberg trials of 1946, when high-ranking Nazi officials were tried for war crimes.

One of the photographs shows Ernst Kaltenbrunner, the leader of the Austrian SS at the camp.

"One of the youngsters [responsible for the photographs], who was 20 years old at the time, Francisco Boix, testified against Mr Kaltenbrunner and brought photos with him to the Nuremberg trials," Ms Sugarman says.

Kaltenbrunner was convicted of war crimes and crimes against humanity and hanged.

Family may never know all the album's secrets

Ana and Bogden Ivanovic and Jelena Ciufo pose in Yugoslavia, 1939. ( Supplied: Annabelle Ciufo )

Ms Ciufo never met her uncle, but remembers family members speaking fondly of the amateur painter.

Despite the hardship he endured, he was a playful man, known by the nickname "Bobo".

Born in Zagreb, he survived terrible treatment by the Nazis, including medical experimentation while he was in Mauthausen.

His family may never know how he came to own the photo album that would help convict war criminals.

Ms Sugarman considers it an important reminder of past atrocities that serves to explain different aspects of the Holocaust.

"It is such a layered story, that it is not only to be seen from the perspective of the victims," she says.

"You want to say: 'Who did this? Who were the perpetrators? Who were the bystanders? Who were the collaborators?'"

This image — not part of the Ivanovic album — shows prisoners who survived medical experiments at Mauthausen. ( Getty Images )

For Ms Ciufo, the historical artefact has gone from a strange collection of images, forgotten for decades, to a startling reminder of the price of intolerance.

Ms Ciufo says that despite not being able to understand the cruelty depicted in the album, she still feels part of it.

"It lives strongly in my memory ... this is humanity, this is us."