On the 20th of July 1969, more than 600 million people - a fifth of the world's population - watched in awe as Neil Armstrong became the first man to walk on the surface of the moon.

In April 1970, the world held its breath as a damaged Apollo 13 limped home after failing to land on the moon. But media and public interest in the Space Race was already on the wane and continued to fade during the remaining missions.

The last man to set foot on the moon were the astronauts of Apollo 17, in December 1972. But even before this, a set of conspiracy theories were spreading, the most radical of which claimed that NASA had faked all the lunar landings - that Man in fact never landed on the moon.

As researchers investigated the photographic evidence, a number of questions arose, leading people to believe that NASA may be hiding something. A leading photo-journalist has cast a sceptical eye over some of the key Apollo photographs - allegedly taken by astronauts with cameras strapped to their chests and using no other light source than the sun - to see how the theory stands up to scrutiny.

This shot of Neil Armstrong and Buzz ALdrin planting the U.S flag on the moon's surface was taken by a 16 mm camera mounted on the Lunar Module.

Aldrin's shadow A is far longer than Armstrong's. Yet the only light on the moon - and the only light source used by NASA - comes from the sun, and should not create such unequal shadows.

Buzz Aldrin stands with the sun shining down across his left shoulder. Although his right side is in shadow, there is too much detail shown on that side of his space suit B. It should be much darker and less visible because the contrast between light and dark is much greater on the moon.

With no atmosphere to pollute the light on the moon, all the photographs should look bright and crisp. But the landscape behind Aldrin C gradually fades to darkness. This 'fall-off' effect, haox theorists say, should not occur on the moon. But the fading effect could have happened because film is less adaptive than the human eye and makes objects seem darker the further they are from the camera.

There is a curious object reflected in Aldrin's visor D. Some theorists think it is a helicopter, others say it is a 12 metre glass structure. NASA claim it is a piece of equipment on the lunar surface.

NASA claims that the strange shape E - in this shot taken from the Lunar Module while it was 95 Km above the moon's surface - is a shadow cast by the Command Module's rocket. But when larger aircraft fly at lower altitudes over the earth, they do not cast such huge and defined shadows.

This shot of James Irwine - like many Apollo photos - show a lunar sky without stars J. Yet with no atmosphere on the moon, stars should be visible. If NASA could not hope to recreate a lunar sky, they may have opted for simple black backdrops. NASA claim that the sunlight was so strong it overpowered the light from the stars.

On the shadow side of the landing module, there are plaques K with the American flag and the words 'United States' quite bright and clearly visible, but the gold foil around the plaques is in near darkness. Studio spotlights highlighting these areas, or technicians retouching the prints, could have caused this effect.

As Alan Bean holds up a Special Environmental Sample Container, the top of his head is clearly in view. But the camera taking this shot was fixed on to Charles Conrad's chest and the ground seems to be level, so the top of the helmet L should not be in this photo.

Shadows visible in Al Bean's visor M go off in various directions, not in straight parallel lines, as expected suggesting that there was more than one light source. The container Bean is holding N is brightly lit at the bottom, yet it is facing away from the light. This may be due to the light reflected from Bean's suit on to the container, but the rest of the container is not so brightly lit.

In this photograph of John Young readjusting an antenna next to the Lunar Rover Vehicle (LRV), there is a marker know as a cross-hair (inset) P, that goes behind the LRV's equipment. These cross-hairs Q, which appear on all the lunar photographs, are made by a screen of cross-hairs placed between the shutter and the film. The bright reflected light may have obliterated the fine line of this one, or it could have happened if the image was retouched.

The foreground shows what looks like the letter 'C' on a boulder R. Is this perhaps an identification letter left on a studio prop ?

The tracks made by the LVR's wheels turn rather oddly at right-angles S. These tracks could have been caused by studio technicians pushing the buggy into place. Such clear tracks and footprints require moisture to form and not appear on the dry lunar surface.

The two leading supports of the faked moon photographs theory come from either side of the Atlantic.

Ralph Rene, an author from New Jersey, argues that Man never flew to the moon. He believes that radiation from the sun is so deadly that astronauts would fry as soon as they got into deep space. In his book NASA mooned America! Rene claims the Apollo pictures were shot in a government studio near the town of Mercury in Nevada.

Englishman David Percy, on the other hand, uses his experience as a professional photographer to put forward the argument that the lighting in the Apollo photographs could only have been achieved in a studio on earth. He also claims to have an informant in NASA - Percy calls him Whistleblower - who has leaked information about the cover-up.

NASA used state-of-the-art Hasselblad cameras for the Apollo Missions. On earth, Hasselblads are used for portrait, scenic, and still-life photography.

The viewfinder is on the top, so instead of holding the camera up to the eye, the photographer looks down into the viewfinder. This was ideal for the astronauts because the cameras were mounted on a control unit on their chest. The image presented in the viewfinder is upside-down and back-to-front, which takes some practise getting used to.

The camera had a 250 mm tele-photo lens. This lens was also fixed focus, so all the astronauts had to do was point the camera in the right direction, and forget about focusing. They also had a cable shutter- release within easy reach of their heavy rubber gloves, which did not allow their fingers to move easily.

Hasselblads took square pictures but most of the photographs released by NASA are rectangular. This means that the picture was probably cropped back on earth to get the best-looking composition with the photograph.

One of the strongest pieces of evidence that NASA did land men on the moon is the 340 kg of lunar rock samples brought back by Apollo astronauts. When the rocks were analysed, geologists found several differences between moon rocks and earth rocks. Some moon samples contained much more iron, magnesium and titanium, but less silica and aluminium, than earth rocks. Other samples were found to be far more radioactive than rocks from earth.

Conspiracy theorists are dismissive of lunar rocks, saying that they could have been made in a high temperature ceramic kiln or collected from unexplored areas of Antarctica.

Certain aspects of the shots - the high-lighted flags, the Lunar Modules without craters, the camera's cross-hair disappearing behind the image, the abnormally distinct tyre tracks and footprints - are difficult to explain away completely. But perhaps the most intriguing question is why the photographs may have been faked, regardless of whether or not Man actually landed on the moon.