Graffiti artwork on display in South Korea has been damaged by a couple who thought brushes and paint laid in front of the piece were for visitors' use.
"They thought they were allowed to do that as participatory art and made a mistake," the head of the exhibition in Seoul told Reuters news agency.
After staff spotted fresh brushstrokes CCTV footage identified the accidental vandals, a man and woman in their 20s.
The untitled piece is estimated to be worth about $500,000 (£360,000).
It was painted by US graffiti artist JonOne in front of an audience in Seoul in 2016.
It has since been displayed at various venues, along with the paint and brushes used in the live performance - which are regarded as integral parts of the artwork.
Kang Wook, the head of the exhibition at Seoul's Lotte World Mall, told Reuters: "We are currently in discussions with the artist about whether to restore it."
Police found and questioned the couple at the gallery. Organisers decided not to press charges and the pair were released.
The incident prompted the gallery to put up a small fence in front of the graffiti with additional signs saying: "Do Not Touch".