A search on Catalda Fine Arts in Google finds loads of references to a famous court case in 1951 where they were taken to court for copying pictures they had no right to copy.
Often they had no access to the original so took copies of copies.
I have little knowledge of art or the value of works of art, but I would say these have little value.
Take them to a local auction house to check.
An example web site detailing the court case:
http://www.coolcopyright.com/cases/fulltext/be llcataldatext.htm