By the time Lisa Kristine rose to prominence as one of few photographers able to provide a glimpse into the lives of people living in modern slavery, she was already well known as a photographer of indigenous peoples.

She’d spent years travelling the globe to spend months at a time immersed in indigenous communities from Bhutan to Kenya. And yet, nothing in her previous experience could have prepared her for her first encounter with modern slavery.

It came at a brick kiln in Nepal, which she visited together with NGO Free the Slaves, a partner of the 50 for Freedom Campaign. There, she came face to face with the inhuman conditions of families working in “bonded labour”, a form of debt bondage that can ensnare generation after generation of victims.

“Enveloped in the severe temperatures, men, women and children were cloaked in a heavy blanket of dust while mechanically stacking bricks on their heads and carrying them from the scorching kilns to trucks hundreds of yards away,” Kristine wrote.

“There were no breaks for food or water, no breaks for toilets. Deadened by monotony and exhaustion, they worked silently for up to 16 hours a day.”

Kristine later went to Nepal’s rock quarries where she saw children carrying slabs of granite as large as themselves down treacherous, mountain footpaths. The slabs were so heavy that the children had cords strapped around their heads to help them carry the weight.

Afterwards, Kristine travelled to Ghana where she descended into the suffocating darkness of the country’s illegal gold mines to meet the men and boys who were forced to risk their lives there. Above ground, she met other children who’d been abducted from their homes to work on the fishing boats of Lake Volta.

The project eventually led Kristine back to her native United States, where she found modern slavery hiding in plain view. On the streets of America’s cities, she met dozens of women who’d been coerced into prostitution and were living in conditions she never expected to find so close to home.

“One of the women I met had been trafficked from a middle-class shopping mall,” remembers Kristine. “Traffickers build up trust over a few weeks and then they pounce—sweeping victims off their feet and into the sex trade.”

Faced with so much misery, Kristine confesses that she was sometimes overcome with feelings of helplessness and despair. But it’s the spirit of hope which shines through in her images and continues to inspire her work today.

“I hope these images will awaken a force in people who view them. I hope that force will ignite a fire, and that fire will shine a light on slavery,” she said.

In January 2012, Kristine spoke about her experiences at a TEDx event in Maui. Her talk was featured on the homepage of ted.com and has since been viewed over 2.1 million times.

You can find out more about her work at her website, lisakristine.com.