The unbelievable snaps appear to show a flying saucer-style craft floating above the ground with a helicopter hovering close by.
The five images, taken in the Californian desert, have been decribed as “the most controversial UFO photos on record”.
The man – known only by the pseudonym ‘Keith Bradshaw’ – has released the images in a bid to discover the truth about aliens.
He took the snaps near the Naval Air Weapons Station China Lake in 2007, but has been too nervous to show anyone until now.
Mr Bradshaw apparently sneaked out to the desert after an old friend working on the Navy base told him about the mystery craft.
He claims he heard a helicopter as he approached the base, before seeing the silver UFO with a number of military vehicles parked nearby.
The UFO hunter – who took off his shirt to blend in with his surroundings – spent 10 minutes watching the ‘flying saucer’.
He said: “This thing would wobble along close to the ground, very unstable.
“Then it would freeze in position, go up to a certain height and sit there for a few minutes perfectly still. It made no noise that I could hear.
“I don’t believe anyone could have been riding on the inside, but I got the idea the helicopter was somehow remotely controlling it.
“It looked like whoever was controlling it was having fun with it, sometimes because they would do little tricks with it.”
He has sent the images to be analysed by some of the world’s top UFO experts, who are divided over their authenticity.
British UFO sleuth Philip Mantle said: “This could turn out to be one of the most controversial UFO photo-cases on record.
“The photo-analysts contacted cannot come to an agreement about these photos. Are they fake or genuine? Who knows.”
Jason Gleaves, an ex-RAF and BAE Airbus division employee based in the UK, said he believes they could be genuine.
But he added: “With technology of today and software, you can’t be 100 percent sure of image authenticity, no matter how good it looks.”
Dr Bruce Maccabee, an-ex US Navy physicist, said: “That is not enough evidence to prove either way that the object was not an unusually shaped drone operating under control of the person(s) flying the helicopter.”
Tobias Lingren of Sweden’s Aviation Authority added: “I’m not sure the military is so stupid to fly in an open space a ‘flying saucer’ if they want to keep it secret but I still have no idea what the object could be.”