Chinese authorities have begun deploying a new surveillance tool: "gait recognition" software that uses people's body shapes and how they walk to identify them, even when their faces are hidden from cameras.
Already used by police on the streets of Beijing and Shanghai, "gait recognition" is part of a push across China to develop artificial-intelligence and data-driven surveillance that is raising concern about how far the technology will go.
Huang Yongzhen, the CEO of Watrix, said that its system can identify people from up to 50 metres, even with their back turned or face covered.
This can fill a gap in facial recognition, which needs close-up, high-resolution images of a person's face to work.
"You don't need people's cooperation for us to be able to recognise their identity," Huang said in an interview in his Beijing office.
"Gait analysis can't be fooled by simply limping, walking with splayed feet or hunching over, because we're analysing all the features of an entire body."
Watrix announced last month that it had raised 100 million yuan ($US14.5 million) to accelerate the development and sale of its gait recognition technology, according to Chinese media reports.
Chinese police are using facial recognition to identify people in crowds and nab jaywalkers, and are developing an integrated national system of surveillance camera data. Not everyone is comfortable with gait recognition's use.
Security officials in China's far-western province of Xinjiang, a region whose Muslim population is already subject to intense surveillance and control, have expressed interest in the software.
Shi Shusi, a Chinese columnist and commentator, says it's unsurprising that the technology is catching on in China faster than the rest of the world because of Beijing's emphasis on social control.
"Using biometric recognition to maintain social stability and manage society is an unstoppable trend," he said. "It's great business."