I agree that having a shot at DIY rock art is a good way to gain a bit of insight into the things. But as ever, I found it raised as many questions as it helped answer. It did definitely help rule out a few things that had been posited as artificial, at least in my mind.

And I agree that it would be very easy to make some fairly convincing replicas. No trouble at all really. I've a couple that have been gathering lichen in my yard for a few years now. I've got pics somewhere, I'll dig them out.