By RNZ

Taggers in Christchurch will find it harder to escape detection in future with the city's adoption of innovative technology to map and track graffiti.

Manager of the city council's Smart Christchurch Programme Michael Healy said the new software analyses each photo of graffiti sent by the public and contractors to identify and catch repeat offenders.

Cleaning up graffiti cost Christchurch ratepayers nearly a million dollars a year, he said.

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"And that's not including the costs incurred by property owners."

The council had looked at international programmes matching and tracking graffiti manually and working with police to find offenders, which cut offending by 50 percent.

"We didn't have the resources to manually review all the photographs coming in - we get 20,000 photographs a year, most coming via the Snap Send Solve smartphone app.

"So we thought: why can't we use software and the images we get to do it automatically and then use that information to work with the police and our graffiti team to make a concerted difference?"

A 12-month trial to test the effectiveness of the Smart Christchurch Graffiti Recognition technology will begin shortly.

"There's evidence that graffiti goes with other anti-social behaviour and has a negative effect on neighbourhoods," Healey said.

"If you can keep on top of that and redirect people, mainly young people, in a more positive direction, that's going to make a difference."

The council commissioned local company Flock Consulting to develop the software.

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Co-founder Hayden Park said one of Flock's data scientists came up with the creative idea of an algorithm that was less about analysing the image than matching shapes and contours.

"We've ended up with a stylistic matching engine that's quite clever and quite unique."

Park said councils nationwide struggled with graffiti and it was hoped others would get on board the project.

"Now that we've done it once, there are some economies we can gain by finding a solution that's going to be cheaper across the country, rather than having one council footing the bill to build this solution."

The "beta version" is ready to go, but Flock and city council nowplan to further develop the software so it can automatically upload images sent by the public and build up the database.