The CIA has laid down a challenge to test if people have the sharp eye and attention to detail needed to make it as an investigator.
Only the sharpest minds make it through the selection process for the Central Intelligence Agency in the United States, which is tasked with gathering and analysing security information from around the world.
Its official Twitter account shared two photos of the same scene, challenging users to spot 10 small differences between the images - but some discovered it to be a trick question.
The tweet read: "Put your observation skills to the test. Can you spot the 10 differences in the photo below? Check back tomorrow to see if you found them all."
Many people tried and failed to find 10, getting stuck just short of the total.
Some of the more obvious changes include a man not wearing a backpack, a missing person, a safety rail which has been removed and a car changing colour.
Smaller details that people missed included a light bulb changing from lit to unlit, and a small gold detail appearing on a building in the background.
But even when the CIA revealed the answers, some spotted two extra minute details which had changed, commenting: "More than 10!"
Eagle-eyed users also found a line of paint missing from the archway of a tunnel on the left, and a badge being added to a car parked in the foreground of the image.
The CIA added a second tweet to say: "How many did you find? If you found more than 10 differences, you practiced good tradecraft.
"Always look for opportunities to learn more."
It proved to be too easy for some, who claimed they completed the challenge in less than a minute. How did you get on?
