Today, the idea of taking a photograph and never seeing the result is hard to comprehend, as we shoot away with our digital cameras or smartphones, instantly sharing photos we take. But wind the clock back to the time when photography was an analogue process, and the delay between taking the picture and seeing the prints could be many months, even years - long enough to forget. And for one roll of film, at least, the wait has been about 70 years.
Camera collector William Fagan obtained a number of film cassettes some years ago, when he bought a Leica IIIa.
And though he knew one contained film, he only recently set out to develop it.
They were made, by the Leica Camera company, at a time when film was sold in bulk reels and keen photographers would load their own reusable 35mm cassette.
As it was bulk film, there was no way to identify its speed.
So Mr Fagan had to calculate the development time using best guesses.
But after consulting with experts, he was ready to go ahead.
His plan worked.
And he now has 20 printable negatives.
"Normally when I develop a roll of film, I have some idea of what it contains," he says.
"In the darkroom, I could see old cars.
"But it was not until I scanned the images that I had a clear idea about the contents.
"I was not sure which of my old Leica cameras the film cassette had come with.
"But I believed it was from a camera from the mid-1930s.
"The first negative which I scanned was the one showing a mid-1930s BMW convertible with what appear to be Bavarian plates (AB 52 3287), on a snowy mountain pass."
Another frame showed La Veduta hotel, on the Julier Pass, in Switzerland.
And research revealed the car is a BMW 315.
Other locations included a High Street in Bellagio, on the shores of Lake Como, in northern Italy (above), and Zurich's Bahnhofstrasse (below), which led Mr Fagan to revise his guess as to the date of the pictures, to the early 1950s.
But it is the people that really interest him.
"The real shock came when I saw the personal photos of the people, a woman and a man with a family pet on a trip around Switzerland and northern Italy," he says.
And he is keen to identify those people so he can pass on the prints.
"Such photographs are usually regarded as very personal mementos of happy times," he says.
"And I really felt that I, as a stranger, should not be looking at them.
"Then I thought again about the fact that no-one would ever have seen these photos if I had just thrown away the roll and had not developed it.
"I thought about the ages of the people in the photos and the possibility that neither of them might still be alive.
"I felt that, even if they were no longer with us, their families might wish to see the photos.
"Then there were further thoughts about why the roll of film, which contained some lovely pictures, was never finished or developed.
"As a keen photographer I have always felt that people take photographs for a reason and that photographs record moments in time which can never be recorded again, as such moments do not repeat themselves."
So if anyone out there recognises the people in the picture, Mr Fagan would love to hear from them.
You can contact him via Mike Evans's website, using the address: firstname.lastname@example.org
Here are a few more shots from the roll of film.