I'm new on these forums (even if somebody could know me from Forvm's discussion boards: Federico M).
I don't know if you already discussed this issue, but I'm just writing to suggest you to adopt creative commons as standard for the non-completely proprietary images of coins. See:
This is not a "new" project: as an example, Flickr is using these licenses as possible standard choices for user: http://www.flickr.com/help/photos/?search=copyright#87
Another useful aspect of using Creative Commons to license one's creation is that Yahoo and Google and other search engines are implementing searches by license: