In China, there is no such thing as a faceless crowd.
Use of facial recognition technology in Chinese cities is reaching a tipping point, and paints a vision of how a person's face may one day soon replace keys, bank cards and even an identity card.
It may also serve as the ultimate tracking device.
Coupled with a fast-growing network of surveillance cameras - industry researcher IHS Markit estimates that China will install 450 million new cameras by 2020 - facial recognition technology has helped cities catch wanted criminals that have long eluded the law.
One instance was at the Qingdao beer festival in August, when 190 suspects were identified over the month-long event. Secondary checks confirmed that 25 of them had escaped from custody, including a suspected mastermind of a prostitution ring who was on the wanted list for a decade.
The authorities are also using facial recognition to name-and-shame jaywalkers in cities from Changsha to Shanghai and Wuhan: those caught on camera would have their faces - and in some instances even their names and part of their address - flashed on giant LCD boards. The system can also specially label repeat offenders.
"Use of facial recognition in the area of public security is already very widespread in China, which speaks to the power and accuracy of the technology today," said Dr Xu Li, CEO of SenseTime, one of the leading Chinese firms in this field.
A 40-day trial in Chongqing this year using the firm's technology identified 69 persons-of-interest. He told The Sunday Times 14 of them were arrested by the police.
Chinese firms, which have already outstripped Silicon Valley in related patent filings last year, have two advantages in this field, said Dr Xu. "In China, we have an edge because there's greater acceptance and embrace of new technology.
"Also, there's a big data bonus: under various situations, such as if we need different types of data to train our systems and improve their performance, we can do so."
How it works
Facial recognition systems work by analysing features that are common to all human faces, such as the distance between the eyes, width of the nose and position of cheekbones, as well as shape of the jawline and chin.
These measurements - more than 80 in some systems - are combined to form a "face print" that can uniquely identify individuals. Today's systems can also add each new face to a database, which "learns" from the data to become quicker and more accurate.
While early face recognition systems could be fooled by photographs or recorded video, the technology has improved tremendously in recent years.
A study by the US National Institute of Standards and Technology in 2003 found that fingerprints and faces provide similar accuracy, provided image quality is well-controlled.
Today's systems employ better technology such as 3D cameras and infrared lasers that work with software to prevent impersonation and offer better accuracy than fingerprints in controlled conditions.
For instance, Microsoft and Intel showed they were able to distinguish between identical twins in 2015, while Alipay's new payment kiosk can identify a user even with thick make-up on or a different hair colour.
But facial recognition technology's strengths are also its weaknesses.
While it is contactless, poor image quality such as photos taken under harsh sunlight or in deep shadow severely affects accuracy, or leads to false rejections.
And while the technology can quickly pick out faces in crowds, simple items such as face masks, sunglasses and scarves still defeat it.
The race is on among various companies to hone the technology further, so that issues such as shadows and odd angles pose less of a problem in the future.
Lim Yan Liang
China has vast amounts of data, useful for improving the accuracy of facial recognition systems. Its 730 million Internet users upload plenty of images daily, while the government has a huge database from the official photo identity card which is mandatory from the age 16 for all of its 1.3 billion citizens.
While privacy advocates might decry what seems like a creeping surveillance state, there is growing acceptance in China of facial recognition as a form of identification.
The technology was key to smoother crowd flows during the hectic Golden Week holiday which ends today. More than 700 million domestic travellers were on the move during the holiday, which coincides with China's national day, and many cities took the opportunity to stress test facial recognition at railway stations, hotels and airports.
In Jinan, for instance, infrared cameras and gate machines replaced human checks at its main railway station, improving passenger flow and cutting down on manual errors, a station officer told Xinhua.
Major Chinese banks are also growing their networks of ATMs that accept a customer's face in lieu of a bank card to withdraw cash.
The Agricultural Bank of China, (ABC) China Merchants Bank and the Construction Bank of China have all been rolling out face-scanning tech at their ATMs. ABC last month said all 3,300 of its ATMs in Guangdong province were equipped with the technology.
Increasingly, the face is also replacing fingerprints and passwords for cashless payments.
Last month, Alipay launched a "smile to pay" system at a KFC outlet in Hangzhou, Zhejiang province.
The system uses technology from another Chinese firm, Megvii, which also counts Didi Chuxing and China's Ministry of Public Security among its clients.
The public's growing exposure to the technology in various fields also means facial recognition is likely to be the next step in China's cashless society revolution, Guizhou Smart City Research Institute researcher Yang Gan told China Daily.
"In the future, payment via facial recognition and mobile payment will be complementary," he said.
Number of Internet users in China, who upload lots of images daily.
Chinese government's database from the official photo identity card which is mandatory from age 16.
New cameras to be installed by 2020.
Then there are the more quirky uses, such as a facial recognition system that controls toilet paper use at the Temple of Heaven, a popular tourist spot.
The technology has also become a mainstay in mobile apps that form China's booming US$3 billion (S$4 billion) livestreaming market.
Besides providing livestreamers with bunny ears and other face-changing filters, the technology will soon be used to serve augmented reality advertisements to viewers, said Mr Yang Xu, general manager of group marketing for Yizhibo, one of China's largest livestreaming apps.
"We also use AI, facial recognition and related technologies for content management, such as to prevent pornography from being shown on our platform," he told The Sunday Times.
Experts see growing acceptance of facial recognition in daily life as inevitable, as it is already a more accurate identification tool than a fingerprint, while also being contactless.