Since being first seen in 1870, unidentified flying objects (UFOs) remain a mystery that humans have not yet explained or approached.
Photographs of UFOs have been taken for nearly 140 years
This is believed to be the earliest photo of UFO taken from Mount Washington, New Hampshire (USA) in 1870.
Another early picture of UFOs in the US in the 1920s.
A mysterious object hovering above a sawmill in Ward, Colorado (USA) in April 1929.
New Year's Day 1939: An American man is unaware of a UFO flying in the back.
A mysterious object shines bright lights in Los Angeles on February 25, 1942.
This photo was taken by an American photographer at Tiensten in Hebei Province in 1942. Some people in the photo seem to be pointing at flying objects.
A Japanese plane flew over the sea in 1943, followed by a black sphere.
This cylindrical UFO was caught in the sky of New York City on March 20, 1950.
An amateur photographer took a picture of a UFO at Passoria, New Jersey state (USA) in July 1952.
UFO appeared in the sky US congressional building in Washington DC capital in 1952.
4 men are watching intently flying objects in the sky of Sicily, Italy in October 1954.
A pilot caught sight of UFOs following the B-47 near Edwards air base in California in September 1954.
One of many photos of UFOs taken in Japan: flying objects appeared in Kaizuka sky in 1958.
One of the famous photos of UFO taken by Joseph Sigel in June 1959 in Waikiki, Hawaii.
Alan Smith, 14, took this picture around 1:45 pm on August 2, 1965 from the backyard in Tulsa, Oklahoma.Another 5 witnesses also saw UFOs change color from white to red and blue.
In the summer of 1966, a flying security officer took a picture of two strange spheres glowing red in the sky of Switzerland's Zurich-Kloten airport.This photo was later announced by Swiss pilot Ferdinand Schmid.
History of secrets about UFOs
