An American artist is being accused of stealing works by South African photographers, who captured the atrocities of apartheid.

CBS News foreign correspondent Debora Patta reports one of South Africa's most revered photographers is Peter Magubane, who documented life in South Africa for six decades. His daughter, Fikile Magubane, said her father was appalled when he discovered Hank Willis Thomas used his images without permission and altered them.

Thomas disagrees that he did anything wrong, telling CBS News that having to ask for permission to use the photographs is tantamount to censorship.

Artist Hank Willis Thomas is accused of stealing photographs from Peter Magubane. CBS News

"It's a dangerous moment when we start to tell people what they can and cannot talk about. What they can and cannot focus on when they're making art," Thomas said.

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Fikile Magubane disagrees, saying as an artist, Thomas "should know better."

"That is total arrogance as far as I'm concerned," Magubane said. "Very shameful, but also very disrespectful."

Thomas also used a photograph from Graeme Williams, who later saw an altered version for sale for $36,000.

"Immediately I just thought well this is stealing," Williams said.

A photograph by Graeme Williams was used by artist Hank Willis Thomas. CBS News

Patta reports South African copyright laws are clear: You may not reproduce or alter an original photograph without the owner's permission. While U.S. laws may not be as stringent, copyright lawyers told CBS News the original works are clearly identifiable in the works by Thomas, which amounts to copyright infringement.

Despite that, Thomas said he's not so interested in the legal debate, and more interested in the moral debate. Patta said he raises the argument that Williams is a white photographer who took pictures of black South African kids without their permission. But Patta said it's important to remember both men risked their lives to document the history of South Africa.

"This was a dangerous place to work so this was not an easy job they did. Graeme Williams, I know, sold that photograph once he made a sum total of $1,000. These men are not wealthy and so I think that's why also they're so hurt. They risked their life to bring these images to the world to show them what was really happening in this country," Patta said.

Patta said this debate must also include an understanding of South Africa's history, which includes black South Africans being dispossessed of their land, right to vote and artwork.

"You have that history of theft, of colonial masters taking artifacts, taking artists works, taking songs and claiming it as their own," Patta said. "If you are going to wound people, if you are going to evoke painful memories of historical theft, and further wound these photographers who risked their lives, and what they did, doesn't that go against your original point of what you are trying to do."

The two South African photographers are considering legal action and a U.S. firm has offered to represent them pro bono. Meanwhile, the gallery where the works by Thomas were being sold said they weren't aware of any copyright infringement but has since stopped exhibiting the works until the matter is resolved.