As U.S.-backed forces continue their fight against the Islamic State of Iraq and Syria (ISIS) for the Syrian city of Raqqa, the terror group's de-facto capital, a new film highlights the vast challenges -- and dangers -- that citizen journalists have faced in covering Syria's conflict.

Matt Heineman, director of the documentary "City of Ghosts," said the story of a battle of ideas between ISIS propaganda and the Raqqa Is Being Slaughtered Silently group, which has documented the Syrian war and atrocities committed by ISIS from inside Raqqa, initially drew him to the project. But, he said, the film for him became much more than that.

"It became a story of these guys being on the run after members of their group were killed," he said. "It became an immigrant story. A story of rising nationalism in Europe, where they eventually settled. It became a story of trauma and the cumulative effects of trauma."

"I really wanted to put a human face to the topic that so often gets relegated to headlines or stats or photos," he added, speaking on "Face the Nation."

Abdalaziz Alhamza, a Syrian journalist and co-founder of Raqaa is Being Slaughtered Silently (RBSS), said it was a duty to show the world the atrocities ISIS has committed.

"First, after ISIS took over our city, they started to spread their propaganda everywhere, they were able to recruit many people and like, we knew that what they were talking about or what they were talking about it were like mostly rumors, fake news," he said.

"We started to watch the international media organizations taking ISIS as a source," he said.

Alhamza added, "We used to work as activist journalists against the Syrian regime and the Syrian government. So we decided to complete our work to be against the Syrian government and ISIS. And we started to report the news."

Heineman called the work the group is doing "truly amazing," and said weapons are not going to fix the ongoing crisis.

"Weapons are not going to fix this issue," he said. "There's a whole generation of children and people all across the world that have been indoctrinated by this ideology. So we as a society, as governments, as corporations need to find a way to combat this and I think the work that RBSS is doing is truly amazing as one step in that battle."

Over the last several days, U.S.-backed forces have closed in on ISIS in the fight for Raqqa.

"I think we're in the first 25 or 30 percent of the campaign for Raqqa," Lt. Gen. Stephen Townsend told CBS News last week. "We're just getting started good in Raqqa."

He acknowledged that U.S. troops won't be leaving Syria any time soon.

"I think U.S. troops will start leaving Syria when ISIS is defeated," Townsend said.

But will ISIS turn into an insurgency when they've lost all their territory?

"I think that's the next stage of ISIS," Townsend said. "We call that ISIS 2.0 -- an insurgency, rural. So I think we'll still be here dealing with that problem set for a while."

ISIS may be difficult to eradicate entirely, but Raqqa was used as an operations base to launch terror attacks on the West -- and the U.S. hopes by retaking the city, it will prevent future attacks, CBS News' Holly Williams reported.