UFO stands for Unidentified Flying Object, and as such UFO's are real and defiantly exist, they just cannot be identified by the viewer. Many people automatically associate UFO with Extra Terrestrial, if they cannot identify something flying - it's an alien UFO.
Photographs of UFO's are investigated and usually identified as a known object such as a weather balloon or aircraft. When this happens it ceases to be a UFO and is reclassified as an identified object. Some objects are clearly hoaxes and are identified as such, some are convincing but on careful inspection are found to be identifiable. There are however a few photographs that cannot be explained.
UFO's in History
Unidentified Flying Objects have been reported throughout history with tales from every continent. Many of these phenomena have been found to be astronomical objects such as comets, bright meteors, planets or atmospheric phenomena such as sun dogs and lenticular clouds. Other historical reports seem to defy explanation, but evaluating such accounts is difficult at best because of inaccurate accounting of the event - some accounts have been exaggerated, whilst others lack details.
Accounts of unidentified objects date back into pre-history. Around 1450 BC, during the reign of Pharaoh Thutmose III, there is a description of multiple "circles of fire" brighter than the Sun and about 5 metres in size that appeared over multiple days. They finally disappeared after ascending higher in the sky.
On April 14, 1561 the skies over Nuremberg, Germany were reportedly filled with a multitude of objects seemingly engaged in an aerial battle. Small spheres and discs were said to emerge from large cylinders.
Modern Sightings of UFO's
The advent of the photographic era has enabled people from all walks of life to capture images in great detail for analysis, however nearly all of them have proven to be hoaxes when examined.
The first modern recorded observation took place in in Copiapo city, Chile, in 1868. Since then reports of UFO sightings have been increasing over the years, peaking in post World War 2 America. The most famous UFO is probably that of [rel post=162]Roswell, New Mexico[/rel], where the US Military allegedly captured a downed UFO.
There are differing types of UFO reported, interestingly they vary in design by time. In the 40's and 50's they were primarily of "flying saucer" or "cigar" shaped, in the 70's and 80's they were primarily tall or round, "chandelier" style (i.e. Close Encounters), and in the 90's -00's they seem to be "black triangle" popularised by the sci-fi show X-Files.
UFO's have also been linked to Crop Circles and Cattle Mutilations and abduction's. They have been the subject of thousands of Movies and TV shows, dating back to the earliest days of the medium. Stories have been published for many hundreds of years.
It is not clear what stories are fact or fiction, but undoubtedly the stories will continue to be told and new ones told. Maybe one day we will have conclusive proof of the existence of extraterrestrials, but for now all we have are nice clear pictures of a cullinders and models, or a very blurry image of possibly a genuine UFO, but it's too blurry to be sure.