The Mellon Foundation funded a study entitled, "Reproduction charging models & rights policy for digital images in American art museums." KDCS undertook this study of USA art museum policy and practice regarding the market for digital resources. 120 U.S. art museums were surveyed, with in-depth interviews conducted at 20 museums. The executive summary and link to the full report can be viewed here.
This is an extension of a 2002 report that looked into pricing policy with U.K. and other European libraries and museums. That report was entitled, "Exploring Charging Models for Digital Cultural Heritage: Digital image resource cost efficiency and income generation
compared with analog resources."
The bottom line is that museums are not charging what they could be (of course) and are giving up opportunities. The reports give recommendations which will undoubtedly create interesting discussions.