In Nigeria fake news can be so outlandish, yet widely believed, that the president recently felt compelled to declare that he had not died and been replaced by a Sudanese body double. Nigeria's fake news can also be lethal.

The stakes are high in Nigeria ahead of Saturday's presidential vote marked by widespread discontent over unemployment, poverty and insecurity in some parts of the country. Officials warn that fake or outdated pictures depicting communal violence trigger retaliatory killings.

Africa's most populous country is so awash in falsehoods posted on Twitter, Facebook and YouTube that 16 media outlets have been collaborating on a fact-checking initiative, CrossCheck Nigeria, to research suspect election claims circulating online.