There’s clearly a discrepancy between the sharpness of the photo and the render, so I should maybe add a slight blur, and/or some sensor noise.
I based the shapes of the stones on real examples, mostly the stones at Callanish. The backplate is my own.
It isn’t a perfect composite, but it’s maybe easier for me to see the flaws since I made them.
The apparent partial transparency is genuinely a coincidence. When you zoom in you can see those shadows don’t align with the background trees. However, it might still be worth repainting the stone textures to remove it.