My wife has 2 photos taken by T. Whittaker. The stamp on the back of both says, "T. Whittaker, 140 Stephen's Green West, Dublin".
One of the photos is believed to be of a brother and sister, born in 1861 and 1866 respectively and baptised in the RC Parish of Booterstown, Blackrock and Dundrum. The parents of these two children were from Stoneyford near Thomastown in Kilkenny. The two children concerned had 3 siblings, all of whom died from scarlet fever between 25 October and 4 November 1874 so I presume this photo was taken after 1874 in or near Blackrock where the family lived.