A woman from the Hausa tribe, with a red mark on her thumbnail indicating she has already validated her voting card, looks at her smartphone while she waits for friends to finish the process, at a polling station located in an Islamic school in Daura, the home town of opposition candidate Gen. Muhammadu Buhari, in northern Nigeria Saturday, March 28, 2015. Nigerians went to the polls Saturday in presidential elections which analysts say will be the most tightly contested in the history of Africa's richest nation and its largest democracy. (AP Photo/Ben Curtis) | picture-alliance/AP Photo/B. Curtis