I believe it has to be a Photo ID
South Africa, under a constitution signed by Mandela in 1996, has a rigorous election integrity system. Voters are required to have valid government-issued IDs to register to vote and then cast a ballot.
And a photo even shows Mandela urging supporters to get IDs.
The photo was captured by an AFP photographer in late 1998 ahead of the 1999 African National Congress elections, according to a caption on Yahoo News.