30 years after it was taken, an expert believes he's solved the mystery behind the 'World's clearest UFO photo'.
Photographs of UFOs are often dark and fuzzy, leaving enthusiasts disappointed and skeptics questioning their authenticity.
But one picture taken in Perthshire, Scotland back in 1990 clearly shows a diamond-shaped object hovering in the sky.
Dubbed the 'Calvine Photograph,' negatives of the picture were originally handed over to Scotland's Daily Record newspaper, who in turn sent it to the Ministry of Defence (MOD).
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Behind the 'alien' craft is a fighter jet, leading some to believe that it was a UFO encounter that was handled by the military.
But investigator and former BBC Horizon producer Simon Holland has his own theory.
In March of last year, the Daily Record reported that the Calvine Photograph was taken by a Glaswegian hotel porter called Kevin Russell.
After Russell's name was shared, Holland spoke about his theory that the image was of a secret military aircraft on a test flight.
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Speaking on his YouTube channel, Holland said: "I was sent the Daily Record story and I think it's fair to say that there are a lot of people out there excited at this exciting development.
"The Kevin Russell mentioned in the story would have the best, first-hand account of what happened and he could help settle this enduring mystery.
"But I do have my own theory on what he photographed."
He believes that British Aerospace was working on a new radar-proof defence system, which included the diamond-shaped ship, and the Harrier jet spotted in the background was escorting the experimental aircraft.
Holland continued: "I think there is an acceptance by many that the photo is not a fake. There was, I believe, a mysterious aircraft in the sky that day.
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"The MOD previously stated, no 'known' Harriers were flying in Perthshire on August 4, 1990. That turns out to be a massive clue to whose they were.
"I discovered that the only other British Harriers were privately owned by BAE Systems, the defence contractor. They used their Harriers as multi-roll defence test platforms, testing BAE advanced technology."
The Calvine Photograph was kept hidden from the public for 30 years, before academic and journalist Dr. David Clarke uncovered it following decades of research.
Dr. Clarke got in touch with Craig Lindsay, a former RAF press officer, who had kept a copy of the photo after the story was looked into back in the nineties.
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Alongside Vinnie Adams, from campaign group UAP Media UK, Dr. Clarke has now ensured that the image will be filed in Sheffield Hallam University’s archives, saying: "It feels good to be able to show this elusive photograph to the world."
Bec Oakes