I wonder.. I believe you can see the wording and carving on gravestones by getting a blanket, covering you and the stone, and shining a torch on the stone at various angles. Yes you look quite odd doing this.
Surely it would work on rock carvings too? Though whether you could also then take a photo I don't know.
(on the gallery: my one and only rock art piece of artistry is languishing in the art department somewhere. They couldn't find it when I last went, although it was said to be definitely there. Not that I'm giving up that easily)