ha! I've found a photo of a UFO

http://www.airphotousa.com/Funstuff/Samples/fullsize/denver-ufo.jpg

After some study I've concluded that it might be a drop of water on the camera lens, or it might be one of those filmy stains that's left when water evaporates from your lens (as seen on many a pair of binoculars). But the site SAYS it's a UFO.

Don't be skeptical just because the URL contains "funstuff," either.