The couple, a man and woman in their 20s, thought paint and brushes laid beneath the artwork were for visitors’ use and contributed black splotches to the piece.
The work, which was painted for a live audience in Seoul by American graffiti artist JonOne in 2016, is worth around $500,000 (£360,000).
The paint and brushes which were used in the live performance are regarded as integral parts of the artwork.
The couple was identified on CCTV footage as the culprits after staff spotted their fresh brushstrokes.
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Kang Wook, the head of the exhibition at Seoul’s Lotte World Mall, told Reuters they were in discussions with the artist about restoring the painting.
The organisation decided not to press charges against the couple, who he said “made a mistake”.
“They thought they were allowed to do that as participatory art and made a mistake,” Mr Kang said.
Since the incident, the painting has been displayed elsewhere, now with a small fence in front of the graffiti with additional signs saying: “Do Not Touch”.
A reprensative for JonOne told ABC News the artist does not plan to respond to the incident.
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