It would not be surprising if a mural on government surveillance that went missing last month turned up for sale on the art market.

The Spy Booth artwork in the town of Cheltenham in England, created by British artist Banksy, was removed from the wall it had lived on for two years. The mural, which attracted lots of tourists, was granted a protection last year by the Cheltenham borough council that ensured that no one could remove the work.

David Possee, the owner of the wall where Spy Booth was featured, and who was once offered more than 1 million pounds for the mural, denies having sold it. He claims instead that it was accidentally reduced to rubble by workmen carrying out repairs.

If the mural does turn up at an art auction, it wouldn't be the first to do so.

Another Banksy mural, Slave Labour, was auctioned for $1 million after it had gone missing from Wood Green neighborhood in northern London. The record prices reached for street art such as Banksy's is a recent phenomenon.

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Banksy's "Slave Labour" — Photo: DeptfordJon

The sale of street art removed from public spaces emerged in the 1970s and 1980s. At that time, the famous charcoal drawings of artist Keith Haring were stolen from the walls of New York's subway stations as soon as they appeared. The growing popularity of street art is partly due to the fashion world, museums and advertising campaigns that have appropriated the artform.

Legally speaking, the sale of street art raises a number of questions. Who is responsible for the protection of street art? Who is the real owner of the piece and who has the right to sell it? In principle, unwanted graffiti and collages belong to the owner of the building they were drawn on. This rule was confirmed by a high court judgment about an ownership dispute over Banksy's Art Buff last year.

The ownership right must be differentiated from the copyright and the right of reproduction. The French street artist Invader was unsuccessful in convincing the criminal court in Paris that removing his work from walls to sell it on the market was an infringement of copyright. He argued that distribution of his work was an act against his will. The court dismissed his claim, saying that the defendant had always considered his artwork an illegal attachment. Furthermore, the artist could not prove that his piece had been taken down with the intention to sell or distribute it.

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One of Invader's pieces, near the Eiffel Tower — Photo: Guilhem Vellut

There is no reliable way to authenticate street art, making the sale of it problematic. Some dealers and auction houses avoid selling street art at all for this reason. Until it closed down, the authentication committee of the Keith Haring Foundation refused to validate any of Haring's drawings in subway stations. Banksy's authentication committee did not certify Banksy's artwork by explaining that the works were never intended for marketing.

Courts will likely continue to hear many more cases about the removal of street art until there's legal clarity about the phenomenon.