A picture of former South African President Nelson Mandela is shown on a giant screen at the First National Bank (FNB) Stadium, also known as Soccer City, ahead of Mandela's national memorial service in Johannesburg December 10, 2013. World leaders from U.S. President Barack Obama to Cuba's Raul Castro joined thousands of South Africans to honour Mandela on Tuesday in a memorial that will celebrate his gift for uniting enemies across political and racial divides. [Photo/Agencies]