While tens of thousands queued to file past the democracy icon's open coffin in Pretoria, social media was buzzing with condemnation of an apparent sneaked photo of the president's face that had been posted online.
"Government is aware of social media activity on the existence or otherwise of a picture of President Mandela lying in state," said an official statement.
It welcomed social media users' widespread condemnation of the act.
"If this content exists, government calls on people not to view it and to delete it from their timelines."
Neither the authenticity nor the origin of the picture could be verified.
It was a grainy, green-tinted close-up of a face resembling Mandela's image, its eyes screwed tightly shut.
Mandela's family had expressly wished that no photographs of the body be released, and people queuing to view the open-top casket were not allowed to bring cameras and were requested to turn off their mobile phones.
"With regard to mourners filing past the casket, government repeats the caution that no photography is allowed," Thursday's statement said.
Twitter users largely denounced the spread of the image, calling it "shameful" and "totally disrespectful".