In putting together the images for Master of Shadows, my publisher placed a permissions request to use a painting from the collection of the Norton Simon Foundation, in Los Angeles, only to be denied. Master of Shadows is a "trade" book — as opposed to an "academic" one — and apparently it's beneath the dignity of the foundation to have works it owns appear in books intended for the general public, no matter how serious. They do make exceptions for fully illustrated art books, I am informed, which means they will license to a publisher like Taschen but not Nan Talese.
I'm certainly glad that an arts organization finds itself in position to turn down money in this economy, but I find the reasoning dubious, based as it is on antiquated assumptions about the publishing industry (the line between trade and academic is blurry) and a false opposition between the "popular" and the "scholarly." I would point out that Rubens (the artist in question) had no qualms about licensing his work to whomever was willing to pay, friend or foe, like them or not. It's also worth pointing out that he spent considerable energy defending his status as a "tradesman" from snobbish aristocrats.