The two images on the Spahill page are the best examples of a matched pair of rock art photographs for a single site I've seen in ages.
I'm not being snide here to Ryaner btw, as it's just as important to show how faint markings can be as it is to show up the motifs themselves. These two pics could not show each end of the spectrum of motif visibility any better. The way in which lighting can make such a difference, be it natural or artificial light never ceases to amaze me. The contrast between the two pics also makes the page look quite elegant, in a very minimalist kind of way.
Good stuff Messrs Ryaner and McLiam, likewise Mr FW, for putting it there in the first place :)