Some older links regarding museums' licensing incomes:
"The most recent [as of 2005] study on this was commissioned by the Mellon Foundation and delivered by Simon Tanner for King's Digital Consultancy Services, Reproduction charging models and rights policy for digital images in American art museums, 2004, which pointed to 56 of 100 museums with budgets over $10 million receiving less than $50,000 annually from digital rights transactions. [...] The Tanner report cited above notes, p. 35, 'Everyone interviewed wants to recoup costs but almost none claimed to actually achieve or expected to achieve this.' And 'Even those services that claimed to recoup full costs generally did not account fully for salary costs or overhead expenses.'"
And in 2009 I took a look at the UK National Portrait Gallery's published figures, see
("The majority of the licensing fees income goes to the cost of raising those fees itself.")