Enjoy my badly drawn map but use this for directions.

First picture can be found by following the path through the tunnel and continuing until you see a large silo. The picture is on the side of the silo.

Second picture is found by continuing the path from the silo, you will find some storage tanks. The picture is in the middle, right side of the tanks.

Third picture is north of the tanks, left side of a giant cross-shaped wall.

Forth is north of the cross-shaped wall in the middle of a large open area on the side of a car.

First picture will be straight ahead from where you spawned, on the giant tree.

The sixth picture is in the centre of the map.
The easiest way to find it is to line yourself up next to the centre log pillars and walk south.
Watch video walkthrough for help.

The seventh picture is south-west of the cross-shapes wall.
The easiest way to find it is to stand at the tip of the most northern wall and lines yourself up with the tip of the western wall and walk forward.
Watch video walkthrough for help.

The final picture is the easiest of the hard achievements.
Simply go to the car where picture #4 was and align yourself with the car so you're facing forward with it. Walk forward until you see the picture on the trees.
Watch video walkthrough for help.