As the year began to come to a close, we asked National Geographic staff who work closely with photography—through the magazine, Your Shot, News, Travel, and Proof—to choose a photo from 2015 that they just can’t stop thinking about. There’s no formula for what makes an image resonate—it can be a piercing gaze, the perfect light, or a tender moment that strikes a chord with our editors. Over the coming days, we’ll reveal the 2015 photographs they found most memorable and why.

At this writing, there have been 28,607 cases of Ebola virus disease and 11,314 deaths in West Africa since the start of the deadly outbreak nearly two years ago, according to the World Health Organization (WHO). Pete Muller