The woman in the photographs had an eventful year. Which year, exactly, is unclear – judging by the number plate on her car and her three-quarter-length cargo shorts, it was sometime between May 1995 and the early 2000s. It’s undoubtable, however, that she had a good time: she went to see the Eagles perform live in concert, travelled abroad and splashed around in a sunlit swimming pool, visited an exotic bird sanctuary, witnessed a snow storm and then, to round it all off, posed semi-nude in her kitchen, exhibiting her nearly bare bum.

She looks to be in her late 20s or early 30s, and registered her car (or bought a car registered in) Leicester. I don’t know her name because she is a complete stranger, although I have now seen 36 snapshots of her life shot on a roll of Kodak Gold 35mm film. I bought the mysterious film on eBay, developed it myself and relished the results.

Facebook Twitter Pinterest The past is a foreign country… a selection of recovered, previously undeveloped photographs

A small but growing number of online hobbyists have been buying used, undeveloped film rolls. Those who sell mystery film often don’t set out to trade in the stuff, instead it’s usually picked up by chance at house clearances, inside old cameras or in charity shops. There are many tragic reasons why these rolls could have been forgotten about – divorce, death, dementia – and many mundane ones: film processing is expensive and it’s easy to set aside a half-used roll to be finished later and simply forget about it. Used film can sell from £1 to £100 on eBay, and more and more people are gathering online to celebrate their hobby. Over the past three years the subscribers to the Forgotten Film forum on the discussion website Reddit have jumped from 822 to more than 3,000 people. The most popular post of all is an image from the 1950s of a person in an anorak framed forebodingly in front of the Niagara Falls – the film was found inside a camera in an antique store.

The interest in buying forgotten film may be related to a boom in “mystery boxes” being sold on eBay. In 2017, popular YouTubers began buying these boxes, collections of unknown and random items bundled together, and opening them on camera. In this environment, sellers are taking a chance by listing mystery film rolls, while buyers are excitedly purchasing a portion of the past.

Facebook Twitter Pinterest One collector estimates he has spent ‘upwards of $10,000’ on rolls of film over the past five years

“I saw an article about people selling mystery bundles of clothing or electronics, and I thought, ‘OK, maybe someone would want them’,” says Diana Bright of the two used film rolls she sold to me for £19.99 on eBay, one of which yielded the photos of the unknown woman I call “Basia”. Bright, 54, from Chelmsford, bought the film “between eight to 10 years ago” at a bric-a-brac sale. A lorry was offloading boxes of items, and Bright believes they may have been the possessions of someone who had passed away. She bought a bag of cameras because her mother was a photographer, and the used film rolls were inside.

“I probably paid about £5 or £6,” she says now. One of the rolls Bright sold came from a Russian camera, though she can’t remember which roll (could this explain my instinct to give Basia an eastern European name?) The film sat around in Bright’s home for close to a decade until she saw the mystery boxes article. “I wasn’t sure anyone would actually buy them, but I had a few inquiries.”

Bright tried to set “a fair price” for the film by looking around for other listings on eBay, and didn’t want to charge too much because of the risk for the buyer. “I tried to be fair because whoever buys them is taking the chance that they might be interesting or the pictures may not be of any interest at all,” she says.

For Levi Bettwieser, a 33-year-old video producer from Idaho, an interest in forgotten film can be both expensive and risky. Bettwieser estimates he has spent “upwards of $10,000” on rolls of film over the past five years, and says he “can get 10 rolls in a row that come out blank” due to the film being degraded.

“A couple of years ago, I was winning and buying every single roll of used film on eBay,” Bettwieser says. “There’s always a feeling of overall excitement that you might get something amazing, something historically viable. Or you might get more cat photos.” Bettwieser now runs a non-profit scheme, the Rescued Film Project, where he encourages people to give him their old rolls which he then develops. “Part of the reason I’m doing it is because I like the idea of being the first person to ever see these images; even the photographer has never seen them.”

It makes sense that people sell old film on eBay – it’s easy profit. Like buyers, sellers can also have an interest in history. Rhonda Craig is an eBay seller from North Carolina who specialises in forgotten objects – she purchases “unusual, unique pieces” from estate sales and sells them online. She has sold used and unused vintage camera film, as well as old photographs. Of the first used film she sold, she says: “I looked at enough of the family’s personal items to know that this was a lovely family, and it made me so sad it was going to be tossed.”

People who list mystery film on eBay aren’t usually selling their own photographs, but strangers’ memories. Yet while selling is low risk for guaranteed profit, buying can often offer little reward. It’s expensive to develop and can often yield nothing. The second roll I received from Bright featured 14 hazy images – only one picture had any visible features behind the blur: a fridge with a child’s drawing stuck on it. Three other rolls I developed were completely blank, and another roll I was excited about was allegedly from the 60s, but instead featured distinctly modern images taken by a person who might have been an art student.

So why exactly do people like Bettwieser invest time and money in forgotten film? “Those last 30 seconds when you’re about to see what’s on the photos, my heart starts pumping a little bit,” Bettwieser says. “It’s the anticipation that still makes it worth it to me.”

In 2015, 35-year-old filmmaker Jack Jewers from London bought an old film from eBay “on a whim” when he was “slightly bored”. He says: “I’ve always been fascinated with archive film and the idea of lost stories.” He bought a film that was advertised as “exposed/undeveloped/1954”, and “didn’t expect anything” to come out. What he found was remarkable – crystal clear images of a family from Evansville, Indiana, seemingly from the 1940s. In one photo a man poses with a cigar in his mouth, clutching the shoulders of a boy in an aviator cap who is in turn clutching a small black dog. After Jewers posted the images on Facebook, other users identified a couple in the photographs as Helen and Charles Weber, a high school teacher and her husband who died in the Second World War aged just 25.

“It was like bringing a ghost to life. It was finding a slice of life that had been hidden,” Jewers says now. When we speak over the phone, he has a box in front of him full of old films he has yet to develop. “I’m fascinated to see what’s there, but also slightly fearful as well. There’s one part of me that thinks, ‘What if there’s something horrible in there?’”

Others have also been lucky with their forgotten finds. Like Jewers, Ben Larsen, a 25-year-old IT worker from Virginia, also first bought an old film on eBay in 2015. He discovered a series of photos of American soldiers in South Korea, taken during the Vietnam war.

“It’s really cool to uncover something that potentially would never have been seen,” he says. Larsen buys and fixes up cameras to resell, and often finds old film which he develops himself. He has also bought undeveloped disposable cameras and he now helps to run Forgotten Film. “Every once in a while, you get something interesting,” he says. “I’ve found birthday photos, a few vacations… but nothing as exciting as that first one.”

In a roll of film approximately 15-20 years old, I uncovered nothing technically significant – a photo of three people playing boules and a bizarrely beautiful image of a Virgin Mary statue in a windowsill. On a younger film – 10-15 years old, though of course it could have been used at any point after then – I found photos of a young girl’s first Holy Communion followed by pictures of dancing dolphins at Loro Parque, Tenerife. Even though these pictures weren’t historically significant, it still felt special and somewhat magical to get a glimpse into a stranger’s past.

“When you’re taking a picture of someone in your house, you think you’re taking a picture of them, but what’s around them tells a greater story,” says Bettwieser. “You look and try and piece together a story of who those people are.” Jewers adds: “There’s something very powerful about seeing the unfiltered faces of people from decades ago. We have no idea about why a moment meant enough for them to record, we don’t know who they were, or what became of them. It’s voyeurism, but it’s also a privilege to open this window into the past.”

Forgotten film also has an added element of mystery – why were these photos never developed? “Basia” is the only person in all 36 of her exposures – whoever was behind the camera remains anonymous. The pictures show happy times, so why was this roll forgotten about?

The trend for developing mystery film may speak to something greater about how taking pictures has changed in recent years. Where once photography was time-consuming and the results precious, we now snap everything. Anyone born before the mid-90s recalls the excitement of dropping off their holiday photos at Boots and waiting a week to see the results. In a way, every roll of film back then was mystery film – most of us didn’t know which pictures would come out, how we were going to look, or which shots would have a blurry finger in the corner, cutting off half the photograph.

Buying mystery film feels like a way not only to uncover the past, but also recapture it. Despite the risks of getting nothing in return for your money (or finding a picture of a stranger’s bum), it’s undeniably exciting.

“I love so many images for so many reasons,” says Bettwieser, when asked about his favourite photo he’s recovered. “I try and look at every image I rescue as if I’m looking at it in 50 years – everything I rescue is history. People hold on to rolls of film for years and years in the back of a drawer, because we all know that pictures are history, whether it’s just a birthday party or not. Pictures are our only defence against time, our only evidence, sometimes, that we ever even existed.”