I can't believe I am reading this Arniep  do you have an idea which direction you are coming from.  You say "the revenue from which goes to ensure the conservation of that work and many others"  How many sites do you imagine displaying the Mona Lisa are contributing to The Louvre, its upkeep and restoration of its collection.  These works are public domain by virtue of their age.  There is no copyright.  which is why so many sites are reproducing them in the first place