Thanks to a link from Vincent Brown for pointing me at this blog. I haven't found the name of the author, a PhD candidate at NYU, but here is an extract from his/her introduction:
Because all cultures, from the most ancient all the way to your own community, utilize symbols and repetitive elements in art. By tracking the use and context of these symbols and elements, we gain insight into the meanings behind them. This is particularly important when we study ancient cultures or those that are considered ‘lost’, but even well known artists often had their own hidden agendas. Michelangelo, for instance, hid precise anatomical drawings in his Sistine Chapel, but these were only recently recognized. How much more is hidden in plain sight? Any image of any kind in any media from any period can be counted. This is true whether it is a relief image on an ancient Egyptian temple wall, a Rembrandt painting, an Etruscan sculpture, or a modern mixed media work.
Below is a concise introduction to the Art of Counting, followed by a complete transcript.