On 16 July, 1969, Neil Armstrong, Buzz Aldrin and Michael Collins became the first human beings to set foot on the moon, in a moment which is widely recognised as one of humanity's greatest achievements. But some conspiracy theorists still aren't convinced that the Apollo space program happened at all, most recently citing an image which they claim shows a "stagehand" on the set where the mission was apparently faked.

Conspiracists have been poring over an image of the Apollo 17 landing allegedly shot in December 1972, which was uploaded to YouTube on 16 November. Entitled "Reflection in a Visor", user Streetcap1 suggests in the video that a figure can seen in an astronaut's helmet. They claim that this is further evidence that Nasa shot the missions in a studio.

This latest video begs the question: almost 50 years on from the launch of the Apollo space program, why are some people still obsessed by the idea that the moon landing were a hoax?

Professor John Naughton, a senior research fellow in the Centre of Research in Arts, Social Sciences and Humanities at Cambridge University, is part of a team which has studied such conspiracy theories since 2013. He commented earlier this year that such beliefs are a symptom of citizens "calling into question our basic trust in democratic societies."

Perhaps surprisingly, researchers don't think that the internet has a big a part to play in their spread - as one might assume. Conspiracy theories can, after all, be traced back to the French Revolution.

What the internet does do is make it easier to create communities in which to share "new evidence" to prop up theories. And the same goes for those attempting to debunk them.

"The internet doesn't make conspiracy theories more persuasive, it actually seems to compartmentalise people," said Naughton. "We more efficiently come into contact with those who hold similar views, but we also mostly end up working in echo chambers. That's the way the internet works at the moment – especially in social media: you end up somewhere where everyone has the same views."

Professor Naughton concluded that: "by themselves, such theories may reinforce political suspicion and prejudice but they're not the origin of it. On the whole, I think it's fair to conclude that the scale of the threat is pretty limited.

"Some varieties, like antisemitism, can cause huge damage, but others are pretty harmless. Does it really matter that some people think the moon landings were faked?"

Tying in with this explanation, a study published by the University of Illinois at Chicago last week suggested that unfounded beliefs live on because "many people do not view it as sufficiently important to form their beliefs on rational grounds," according to lead author Tomas Ståhl of the University of Illinois at Chicago.

And because people cling on to being able to question democratic societies and share their views in echo-chambers, reasonable explanations go ignored. Conspiracy theorists claim that the moonscape in the footage is too static to be real; that shadows in the images point in inconsistent directions, and that if it was broadcast on TV the crew must have been accompanied by camera operators.

It seems more likely that the background wasn't painted rather that the mountains were 15 miles away from the astronauts. And a film crew on Earth shot the footage with an automatic camera. Besides, if it was faked some 400,000 Nasa personnel would have had to remain silent for half a century.

Yet, the moon landings live on as one of the most popular conspiracies alongside whether 9/11 was real, and if aliens live in Area 51.