I concur with Ron’s posting. Also, it is good to keep in mind that large museums and/or cultural institutions do their own high resolution/ professionally executed photography of their collection(s). These are mainly master paintings that frequently visitors could purchase a poster or a postcard in the gift shop and creates a profit for the organization. When visitors take small portable digital cameras and record digital images on their own (as it’s done all the time in museums nowadays all over the world) is hard to monitor and keep track which instititions/ guards allow these pictures and who don’t. A decade ago, I have heard Canadian scientist Stefan Michalski talking about this issue of “photography in museums” and explaining in a training re: light – UV radiation damage on objects course that these measurements are a very specific policy that many museums then follow to make a revenue from their collections rathers than a real threat and/or risk to the paintings (objects) themselves. Hope this will clarify this issue.