To be completely fair, we don't know that it was staged just for the photograph. We don't know who moved the cannonballs, or why they moved them. All we know is that there are two photographs, and that the one without the cannonballs on the road came first.

we can infer a little bit more than that. The framing of the two photographs is exactly the same (look at the two rocks in the lower right hand corner), and so that camera was almost certainly not moved between the frames. That seems pretty improbable to me if the cannonballs were actually delivered by cannons.

On the other hand, he could've taken a photo before the road was cleared for travel, no?

I suppose that is possible. But then I'd expect to see canon balls somewhere like by the side of the road. Why take the trouble to move them all entirely out of frame?

While an interesting investigation, I have to wonder why it took over a decade to think to compare the non cannonball details in the photos to figure out which came earlier..

I guess hindsight is 20-20 but does kind of seem like an obvious place to look, no?