For about two years, photographer Levi Bettweiser has been hunting for old, forgotten film to develop.

"You're always flying blind when it comes to rescued film," he says. "You have no idea what you're going to get." It usually ends up being run-of-the-mill family shots: birthdays, Christmases, vacation snaps. But then a contact phoned him up last year and told him about a batch of 31 undeveloped rolls of film he found at an Ohio auction.

"Obviously I wanted to know, like, 'Tell me everything you know about this batch of film. Where did it come from? Photographer? What did you learn when you were there?'" Bettweiser says. "And he had absolutely no information."

They turned out to be a trove of World War II photos that turned Bettweiser's Rescued Film Project into a sensation.

(For another stunning collection of war images, check out "Photos We Remember" from LIFE magazine's WWII archive.)

"When it started, it was just me kind of walking around thrift stores in my local town here, in Boise, Idaho," Bettweiser says. Developing the rolls he found was a hobby, slowly buiding up to around 5,500 images. But after finding the war photos and creating a video about them, interest in his project has "skyrocketed."

"It really kind of changed the perception of a project into more kind of a historical archival project," Bettweiser says. "It always kind of had that undertone, but the fact that it's all centered around some major event that has impacted so many people kind of really brings it home for a lot of people."

Donations — both in film and money — have come pouring in, and Bettweiser hopes to turn the project into a kind of crowdsourced history book.

"I would like it to be an archive that is searchable," he says, "a database that you can search and find and everyone can collaborate and kind of research and tag ... really just kind of more document our history from a perspective that's never been seen before."

Bettweiser thinks that's why many people he speaks to end up having undeveloped rolls of their own. "People, I think, inherently feel that these things are too important to toss out, so they've been holding onto them," he says. He's betting his collection is "just the tip of the iceberg."

This image is Levi Bettweiser's favorite from among 31 rolls of World War II film he recently developed. Credit: Courtesy of the Rescued Film Project

But he's also concerned. "I am actively searching and [film] is just not as available as it used to be," he says. "It does degrade and it does go bad and people don't realize what it is and they toss it, or they process it, or someone less experienced processes it and it doesn't turn out."

So while he's making his own slow dent in the world's forgotten film, Bettweiser says he's "worried that we're running out of time."

Here are some of Levi's recovered World War II photos. To see many more and browse the rest of the archive, go to the Rescued Film Project.