Here's the set-up: a helicopter is raising a diver up out of the ocean when suddenly an immense great white shark jumps out of the water for a quick (and fatal) bite. Seem unbelievable to be real? It is.
Here's the original letter:
Date collected: 8/12/2002
Although this looks like a picture taken from a Hollywood movie, it is in
fact a real photo, taken near the South African coast during a military
exercise of the British Navy. It has been nominated by Geo as "THE photo of the year".
This is an out-and-out hoax. According to National Geographic (which was named in another variation of the hoax e-mail), the photo is actually a composite of two separate photos -- one of a great white breaching the water off the coast of South Africa, the other of a helicopter near the Golden Gate Bridge in San Francisco.
You can read their full debunking here: