Police say the images they get of car number plates from thousands of cameras can be used "for any number of purposes".
The extensive use of automated number plate recognition (ANPR) by police last year sparked a legal challenge which is ongoing.
Officers tap into either of two privately-owned ANPR systems several hundred times a day, documents have shown.
"The images can be used for any number of purposes and an extensive list does not exist and so cannot be provided," technology assurance chief adviser Dr Andrew Chen said in response to an RNZ Official Information Act request.
"Your request for a list of the 'full potential range of uses' and 'actual range of uses' is therefore refused."
Police mostly used the AI-driven tech to corroborate existing evidence, place vehicles at times and locations for an investigation, and as supporting evidence in criminal cases, Chen said.
A police technologies list described it as a "retail crime intelligence platform".
Chen said the image captured could be less important than the signal there was CCTV footage of a crime at a certain spot, say, petrol theft.
Plate numbers were captured by live CCTV, and officers - many thousands of whom have authorised access to the systems run by Auror and SaferCities - could access the video and a still image.
"If the camera is in an area where vehicles are stationary (eg, petrol station forecourt) then a still image often includes occupants in and around the vehicle," he said.
"This is less often the case with moving vehicles due to the higher angle of the capturing camera."
Police were forced to audit their use of ANPR - and found very isolated cases of misuse - and introduced better training, two years ago.
Their ANPR policy asserts that an officer should consider getting a production order - similar to a search warrant - if they want to use the private systems "on numerous occasions to predict where a vehicle is likely to be".
It contains a caution to an officer trying to locate a vehicle in real time, that "this is likely to constitute tracking activity" and must go through a special approvals process. This limits tracking to when there is a risk to life of safety, or police have a tracking warrant, or other authorisation for tracking.
Chen was previously an independent researcher who police used to critique their surveillance and biometric systems, and advances in emerging tech.
rnz.co.nz
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