Confirmation that these slides were signed by Frederick H. Evans can be seen at a surprising source: a signed photograph by Evans, of Aubrey Beardsley, is on display at the Musee d'Orsay in Paris, France. A copy-protected image can be seen on the museum's web site. Clicking on the image, then on the magnifying glass symbol, will provide a clear view of Evans' signature. A screen-capture of the signature is included.
