S. Africa election body urges responsible 'selfies'
US President Barack Obama (right) and UK Prime Minister David Cameron pose for a selfie with Danish PM Helle Thorning Schmidt as US First Lady Michelle Obama looks on during the memorial service for Nelson Mandela in Johannesburg on December 10, 2013 - by Roberto Schmidt
"Voters are reminded that it is an offence to take and/or publish photographs which reveal a person's vote on a ballot paper," said a statement on Sunday.
The Independent Electoral Commission (IEC) says the offence is punishable by a fine or imprisonment of up to a year.
The organisation said exuberant expatriate voters around the world had already posted pictures of their marked ballot papers on social media.
South Africa goes to polls on May 7 in the fifth democratic elections after the fall of apartheid in 1994.
While the IEC said it was committed to monitoring the regulation, it admitted that it would be difficult to remove cameras or mobile phones from every voter before entering the voting booth.
Social media networking is popular in South Africa, with a latest study in March showing that Johannesburg has largest number of active Twitter users in the continent.