The image was reportedly taken by amateur photographer Fabian Romano at a Macachín airport in La Pampa, Argentina.
According to the uncorroborated story that accompanies the picture on dozens of cryptozoology websites and blogs, the photographer spotted the fast-moving "being" but was only able to take a single photo before it flew away.
He reportedly sent the photo to local UFO study group which decided it showed a creature of "high strangeness" and forwarded it on to the police.
The blurb with the picture claims that officers used high-tech equipment to enhance the image, revealing that the animal had eye sockets and a beak. The special criminal division estimated that the creature could be up to 2ft 7 in tall, it is claimed.
But the story have been met with scepticism among experienced photographers, who point out that it would be impossible to tell the size of the object without knowing how close it was to the camera.
More mundane and plauside theories include that the photo is a long exposure shot of a bird, or an insect that flew too close to the camera.
"The legs make me think it's some kind of grasshopper or locust," said one commenter on the Boing Boing blog.