AI to help churches and castles fight wave of graffiti and vandalism

Artificial intelligence could become a crucial weapon to deter graffiti vandals from defacing churches, castles and monasteries, after historic sites experienced a dramatic increase in such attacks over the past year.

Historic England is pursuing a pioneering project that could see AI identify culprits from their tags, track their movements by matching graffiti in different areas, and analyse paints to establish where they obtained their spray cans.

Stopping the vandalism could not be more urgent. In the past year, heritage organisations have become a prime target, according to research published on Sunday by Ecclesiastical Insurance, a specialist in the heritage sector.

Its crime survey found that as many as a third (32%) of heritage sites have been defaced by graffiti, an increase of 9% on the previous year.

In April, vandals targeted historic Linlithgow Palace in West Lothian – birthplace of Mary, Queen of Scots – spray-painting graffiti across walls, flagstone floors and the 16th-century fountain. In January, they hit Rochester Castle in Kent – one of the nation’s most imposing Norman fortresses, whose construction began in 1087 – spraying graffiti on the walls.

Spray paint on Holy Rood church in Swindon.

Mark Harrison, head of heritage crime strategy at Historic England, told the Observer: “We’re at the cutting edge of tackling this problem. These are heritage settings that belong to all of us and graffiti is criminal in every sense. It’s persistent and pervasive. It causes distress and affects the public’s sense of wellbeing, which is a really key indicator of how a community feels about itself.”

He is collaborating on the project with Prof Robin Bryant, director of criminal justice practice at Canterbury Christ Church University, who is an expert in artificial intelligence.

The problem is that an initial case of graffiti often encourages further occurrences. Removing it from ancient stone is complex, as the paint leaches, often leaving a permanent, ghostly stain.

The AI exploration extends to its potential use in identifying lead that might have been stolen from a church roof – another tool for law enforcement officials and scrap dealers, requiring only an app on a smartphone.

Harrison said: “Go on to Google Play or the App Store and you can get apps that identify plants, trees and rocks. It’s exactly the same process. We’ve been having early conversations about how we can use this technique to help us identify graffiti artists, who have got a very distinct style and use certain types of colours. But the human eye and brain can only deal with a certain amount of information.

Heritage crime officer, PC Ashley Tether, looks at the graffiti on the city walls of Chester.

“To the human eye, graffiti may look similar, but to the machine it might be quite distinctly different. If you’ve got 100 tags in a neighbourhood, that could be one person in one evening. If it’s left to linger, it just shows people this is a safe place to tag.”

He added: “Working with manufacturers, we might be able to get it down – using the AI imaging – to say what brand of paint it is. Working with retailers, we can see if we can reduce the source.”

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Bryant said that AI offers the possibility to link offences together to the same offenders: “That, in classic policing terms, is normally a very good start in terms of an investigation.”

Linlithgow Palace.

He added: “The recording systems of the police are not geared up. There are some specific heritage crimes which are recorded, such as the illegal dealing in cultural objects. But they’re very rare. The problem is that most heritage crimes are theft or criminal damage and, while these are obviously recorded by the police, there are no specific codes for offences such as criminal damage to a historic building caused by graffiti.”

Other historic sites blighted by graffiti include the Charterhouse Heritage Park, the nation’s only Carthusian monastery with surviving interiors. It dates from 1381 and was given to the people of Coventry in 1940. Emily Thorpe, its general manager, spoke of the distress of seeing graffiti repeatedly sprayed over its 14th-century walls: “It’s a complete and utter lack of respect for how important it is in our history.”

Cleaning the graffiti costs a huge amount of money, she said: “Historic England are helping with some training for us. We have a large bank of volunteers, but you need specialist skills and equipment. It almost feels like a losing battle.”

Harrison said that the “natural surveillance” of the public through Heritage Watch – a neighbourhood scheme specifically for historic sites and buildings – is “a good deterrent”. “Linking traditional community measures alongside the new and emerging technologies has got to be a glimmer of hope for us, hasn’t it?”

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