An interesting one......
I suppose any photo copied directly from this site would be of fairly low quality and therefore its uses by others would be ltd but, as pointed out in the article, it is difficult to be comfortable with the fact that someone else is making money from your work (even if the work was never intended to provide income to the artist).
Could this be addressed by preventing access to photos on the site until after log-in (ie you must be a member to view/ copy them)? Exisiting and new members are required to register their agreement to the terms and conditions of the site, which could be amended to prevent the use of other's pictures for profit??