The trial is happening because the commissioner asked Foodstuffs North Island to show evidence facial recognition technology was a justified way to lower retail crime.
Foodstuffs is proposing to use FRT to scan and make a biometric template of each shopper as they enter the premises to see if they match a watchlist of people identified with repeated harmful behaviours.
It follows 4719 incidents of retail crime reported across Foodstuffs stores in the last quarter of 2023, including 513 trespass breaches - up 52 percent on the previous quarter.
Foodstuffs North Island chief executive Chris Quin said the trial was important because the company hoped to establish whether facial recognition would keep staff and customers safe without compromising their privacy.
"Shockingly, one of our security team was stabbed recently and our people are being punched, kicked, bitten and spat at. We're seeing over 14 serious incidents a week, including an average of two assaults," Quin said.
"All too often it's the same people, coming back to our stores despite having already been trespassed, committing more crime, and often putting our team members and customers at risk of abuse and violence."
Facial recognition had the potential to help by identifying repeat offenders when they tried to come back into stores, he said.
All images in the facial recognition would be instantly deleted unless a person had committed a crime, been aggressive, violent or threatening towards workers or customers or had actively assisted in such harmful behaviour. "This is a high threshold."
The trial starts today across 25 stores over six months and the data will be used to decide whether or not to roll-out the technology further.
Privacy Commissioner Michael Webster thinks the technology is something all New Zealanders should be concerned about because of its privacy implications and he fears it is not a proven tool to reduce harmful behaviour including violence in supermarkets.
"New Zealanders deserve to shop for their milk and bread without having their faces scanned unless it's really justified.
"We wouldn't accept being fingerprinted and checked at the door before shopping for groceries - that sounds ludicrous - but FRT is a similar biometric process that is faster, machine-run, happens in a nanosecond, and creates a template to compare your face to, now and in the future," he said.
He is also worried about what it means for Māori, Pasifika, Indian and Asian shoppers, since the software is not trained on the New Zealand population.
"I don't want to see people incorrectly banned from their local supermarket and falsely accused," Webster said.
The commissioner will consider if any further action is needed to protect New Zealanders' privacy during the progression of the trial.
"The trial itself is not without risk given the effectiveness of the technology and the operational protocols are untested in a supermarket setting. The franchised nature of the Foodstuffs North Island operation also means that individual owner-operated stores who participate in the trial are responsible for decisions about what they do and how they use the data they collect. This is another reason for keeping a close eye.
Unmatched people's images would be promptly deleted following feedback from the Privacy Commissioner's office while matched people would be banned or removed from stores.
In some cases the police would be involved.
Use of technology needs to be 'fully justified' - privacy commissioner
Webster told Morning Report he would be using his powers of inquiry under the Privacy Act to keep a close eye on the trial.
"We'll be monitoring to see if it does actually result in a decline in numbers of violent incidents at supermarkets, which is obviously one of the aims from it."
His office would also be looking at the assessment completed at the end of the trial by the independent evaluator to check that it had delivered what was intended, he said.
"As a general proposition, we're not in the business of banning technologies but ensuring that they're used in an appropriate and safe way, so that their use is fully justified - that's what our legislation, or act, asks us to keep an eye on."
"That's why this trial is so important."
Webster said his office had the power to issue a compliance notice to an organisation directing it to stop using technology in some instances.
"At the end of the day, if, in our assessment we consider the use of ... privacy-intrusive technology is unlawful, we can issue a compliance notice directing an organisation to take steps to stop using it in that particular way."
"I understand businesses' concern to protect their staff and customers and I want people to be safe as they shop and they go to work, but that's why we need to be really careful to analyse the data that Foodstuffs has and will capture over the trial, to see what sort of incidents are happening."
Foodstuffs North Island had "literally, I understand, millions of customer visits every week and a relatively small number of incidents a week".
"So we need to be careful that we when we look at the data we're doing a full and thorough analysis of what actually is happening."
When Foodstuffs announced the trial in December 2022, it said existing FRT would be turned off awaiting its outcome.
