They're some of the most iconic cover photos ever taken: a geologist silhouetted against a wall of flaming lava, a majestic Kalahari lion braced against the wind, a young Afghan girl staring boldly at the camera from beneath a tattered shawl. What did it take for National Geographic photographers to get those shots? And what has become of the people and places they captured then? Nat GeoĆ¢??s Most Amazing Photos reveals the stories behind National Geographic Magazine's most…