| National Geographic photographer and conservationist Joel Sartore is a man on a mission to create portraits of the world's wildlife species, before they disappear forever. Started in 2006, his multi-year project -- called "Photo Ark" -- has sent him to zoos in 40 countries around the world in an attempt to photograph 12,000 captive animal species. He's just reached the halfway mark, capturing 6,000 photos. For the first time, in this month's issue, National Geographic has featured 10 different images from "Photo Ark" on multiple covers. Sartore joins "CBS This Morning: Saturday" to discuss his inspiration behind the project, how he photographs the animals and some endangered animals behind the camera.