Paul Trent's Flying Saucer
This example was recommended by Mark Harris.
On 11 May 1950, Paul Trent took two photographs of a flying saucer. At the time, the term Unidentified Flying Object—or UFO—was not in use. The photographs were initially displayed in a local bank before being published in a local newspaper. On 26 June 1950, Life Magazine published the photographs. The Trent's maintained until their deaths that the photographs were not faked.
I find the evidence that the photographs were faked to be convincing enough to include Mark Harris' recommendation on this website. But, more importantly, asking students to review the evidence and arguments concerning the photographs is a valuable activity to advance critical thinking.
Suggestions for Further Reading
"Farmer Trent's Flying Saucer." Life Magazine. 26 June 1950.
Killen, John. "Past Tense Oregon: UFO Photos Taken Near McMinnville in 1950 Still Raise Questions." The Oregonian. 12 May 2015.
Sheaffer, Robert. "The Trent UFO Photos—‘Best’ of All Time—Finally Busted?." The Committee for Skeptical Inquiry. January/February 2015.