It is very difficult, even impossible, to make decisions about authenticity without seeing the work in person. Some museums offer expertise as a service to their communities but only when the work of art can be studied in person. Research begins by consulting a catalogue raisonné (listing and description of all of an artist’s output). Some catalogues raisonné include information about copies and forgeries. The standard index to these specialized and very useful reference works is Timothy Riggs, The Print Council Index to Oeuvre-Catalogues of Prints by European and American Artists (New York, 1983). An expanded and up-to-date version of this resource edited by Nicole Simpson is now available on-line at this site (select “Search Oeuvre Catalogues” above).