In a candid moment captured by AFP photographer Roberto Schmidt, Denmark's Helle Thorning-Schmidt can be seen holding up her smartphone, with Obama lending a helping hand, as they pose for a picture with David Cameron, all three of them smiling broadly in their seats at Soweto's World Cup stadium.
First Lady Michelle Obama, sitting to the left of her husband, does not join in with the lightheartedness, keeping her eyes firmly trained on the podium where world leaders were paying tribute to South Africa's anti-apartheid hero Mandela, who died Thursday aged 95.
"There should be a moratorium on 'selfies' during memorials and funerals, no?" tweeted @JeffryHalverson.
"Is This The Most Important Selfie Of 2013?" headlined the US-based social news website Buzzfeed, noting that Michelle Obama seemed "not amused" by the impromptu photoshoot.
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A photo of the leaders photographing themselves was featured on the front pages of British media such as The Times, The Daily Telegraph and the Daily Mirror.
"All of it serves as a reminder - as if we needed one - that even the best-laid plans of politicians tend to veer wildly off course in this age of social media," the Post story said.
Cameron's Downing Street office said it had "no comment" on the photo, while the White House also made no comment. There was no immediate reaction from Copenhagen.
A selfie is defined as "a photograph that one has taken of oneself, typically one taken with a smartphone or webcam and uploaded to a social media website".
The AFP photographer who captured the leaders in their group shot said his picture showed the dignitaries in a rare unscripted moment.
"It was interesting to see politicians in a human light because usually when we see them it is in such a controlled environment. Maybe this would not be such an issue if we, as the press, would have more access to dignitaries and be able to show they are human as the rest of us," he said.