This is a full length image of Katherine Mackay (Katherine Alexandra Duer (US1797spouse1)). We know that it is dated circa 1904 since a crop of this photograph> is accompanied by the caption "circa 1904." Still another crop of both images shows her demi-parure of emeralds as well as the diamond pendant at the end of her chain.
See Harbor Hill, Clarence Hungerford Mackay's Mansion.
