It's not an entirely subjective evaluation - there are published scientific criteria ( http://www.eng-h.gov.uk/mpp/mcd/cupring.htm ). But what about the 'drilled stones'? If a hole has been made to hold a shaft, such as in one of the 'battle axes', then it's not considered Rock Art. It's an implement. But what if an identical hole has been made in a large boulder ? Maybe the hole was made to take a pole for a banner - is that Rock Art ?