After picking up your camera from the car and starting your hike through the woods, make sure to take pictures of ravens in the trees. The camera focus(white lines suggesting a square) will turn green when they're in shot.
There are six circles in the lower right corner when using the camera, and these will fill up for each photo of a raven you manage to take. Once all six circles are filled, you'll receive the achievement at the end of the game.
There are more than enough ravens to find, so you don't have to worry about missing them.