A cryptocurrency project described as being "dystopian" has been launched by AI entrepreneur Sam Altman.
Worldcoin gives people digital coins in exchange for a scan of their eyeballs.
In sites around the world thousands of people queued to gaze into silver orbs on day one of the project's full launch.
The BBC visited a scanning site in London where people received free crypto tokens after going through the process.
Mr Altman, the chief executive of Open AI which built chat bot ChatGPT says he hopes the initiative will help confirm if someone is a human or a robot.
"Worldcoin could drastically increase economic opportunity, scale a reliable solution for distinguishing humans from AI online while preserving privacy," Mr Altman claimed in a launch letter on the company website.
Worldcoin also claims that its system could pave the way for an "AI-funded" universal basic income. But it's not clear how.
The concept of a universal basic income sees all citizens paid a set salary regardless of their means.
The first step in this crypto utopia as laid out by Worldcoin though relies on getting millions, maybe even billions, of people to scan their irises to prove they are a human.
Since testing of the scanners began two years ago, Worldcoin says more than two million people have been added to the crypto database in 33 different countries.
According to the company most sign ups have happened in Europe, India and southern Africa.
Despite the company's American foundation, the crypto coins are not being offered to US citizens due to regulatory concerns.
Now that the project has fully launched and the crypto tokens are available to claim and to trade, it's expected to grow even more popular.
Worldcoin posted a picture online of people queuing at a site in Japan and said it plans to roll out 1,500 Orbs in locations across the globe.
The BBC went to try it out at a pop-up site in east London and found a steady stream of people turning up.
The process starts with scanning your face and iris to prove you are a person. It takes about 10 seconds to stare into the Orb's camera lens and wait for a beep to confirm it has worked. Interestingly the Orb operator says the silver ball used to talk to users – but customer feedback described it as "creepy" so they removed the voice.
The next step is that your iris scan is given a unique number which is checked against the giant database to make sure it's the first time you've done it. If so, the ball beeps again and you are now on the database along with 2.06 million other humans at the time of writing.
25 free Worldcoin tokens are awarded on completion which are currently valued at roughly $2 (£1.56) each. The BBC will sell the coins once they are received and donate any money to Children in Need.
By the time the BBC left the pop up site, 13 people had been scanned. All were men in their 20s and 30s.
"I came after seeing Sam Altman tweeting about the launch," said 37-year-old Moses Serumaga.
"I saw that you could get some dollars for it so I thought why not? It could die like other crypto projects or it could be a big thing and go up in value. I didn't want to miss out," he said.
23-year-old Tom also scanned his eyeball but said he didn't do it for the money as he doesn't think the value of the tokens will rise.
"I don't think that amount of money is enough of an incentive unless you live in less developed nations and I don't think there's much possibility of it going up further really," he said.
The scanning process has proven controversial with reports criticising some of the tactics used by orb operators who are paid in commission, with particular concern over those getting sign ups in poorer nations.
Privacy experts also worry that sensitive data gathered from scanning a person's iris might get in to the wrong hands, even though Worldcoin insists that no data is stored.
Vitalik Buterin, the co founder of cryptocurrency network Ethereum, responded to the Worldcoin launch expressing excitement about the project but also issuing a warning about its potential pitfalls.
"On the whole, despite the "dystopian vibez" of staring into an Orb and letting it scan deeply into your eyeballs, it does seem like specialized hardware systems can do quite a decent job of protecting privacy," he said.
However, he also says that relying on the specialised orbs to carry out the scans could give Worldcoin too much power and make it hard to get the world on-board.
Twitter founder and crypto enthusiast Jack Dorsey tweeted an apparent criticism of the project, describing its mission as "cute", and adding the dystopian warning: "Visit the Orb or the Orb will visit you…".
Mr Altman welcomed criticism, saying online that "haters" give his team energy. But he admitted the project was ambitious.
"Maybe it works out and maybe it doesn't, but trying stuff like this is how progress happens," he tweeted.
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