Alan:
The difficulty is, even an economist can't prove a causal link between
increased eyeballs on the images and more museum visitors. You would have
to stand at the door and ask every incoming visitor Are you here today because
you saw or downloaded an image of a work in our collection?
Good point. This is where (by recording link-throughs) a cause-and-effect could
actually be proved, and revenue credited to the source (the online image).
Without any recordable connection between that source and that sale, it's
difficult for our hypothetical economist to prove that the source
