View the most popular Photo of the Day images from 2011, featuring Namibian thorn trees, a whitetip shark and diver in the Bahamas, a birch-covered boulder in the Adirondacks, Dubai skyscrapers ...

In honor of Earth Day, National Geographic is selling prints of some ... Read through the captions to discover the story behind each photo.

"I didn't think the photograph of the girl would be different from anything else I shot that day." Steve said to the National Geographic. However, this photograph became perhaps ... living back in ...