The law concerning the reproduction of works of art is unambiguous: the owner of the physical item does not own the right to copy and reproduce it. The copyright or right to reproduce a work of art either belongs to the artist and his/her heirs, or to everybody when the work is in the public domain. However, a large number of museums use their property rights to assume a copyright, i.e. a right to reproduce works of art. These illegal practices are the result of choosing a business model based on the desire to cross-subsidise the upstream market of the services provided to the public with the benefits obtained by monopolising the “downstream” market of the copies or reproductions of works of art. The objective of this paper is to show that this is not efficient. We argue that this strategy conflicts with the mission upheld by museums and prevents certain externalities from circulating in the society.