The unbelieavable picture - and it is unbelievable - was captured by Martin Le-May, an amateur photographer in the UK.
Mr Le May was out walking with his wife in Hornchurch Country Park, in Essex, when he heard a distressed squawking.
"I saw the flash of green. We trained our binoculars and it occurred that the woodpecker was unnaturally hopping about like it was treading on a hot surface.
"The bird was about 50m away from us and took off just as I lifted the camera up. Originally, I thought I was just taking a picture of a green woodpecker flying. Then I realised it had something on its back."
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The image captured the bird's fight for life after the predatory weasel jumped onto its back and attacked it.
"Suddenly it was obvious it had a small mammal on its back and this was a struggle for life."
The bird was around two metres off the ground when Mr Le-May caught it on camera. Happily, it managed to shake off the weasel and fly up into the trees.
The picture became a sensation when it was circulated on social media, with some Twitter users suggesting it could not be real.
But Matt Binstead, head keeper at the British Wildlife Centre, said: "You can tell it's a real photograph.
"A female weasel is not much bigger than a packet of Polos but they are quite ferocious little predators and will prey on things much bigger than themselves - their normal diet is mice and small mammals but they can go for small rabbits.
"It's quite unusual for them to go for a bird but green woodpeckers forage on the ground. I imagine the weasel gave it a go, jumped on its back and then the woodpecker took off."
It has caused the internet to go mad and create enough memes to fill up Facebook.
Here are some of the best: