Carl's father, August Hentschel (b. 1833), was a photographer, a naturalised American married to Olga Hentschel (b. 1844). All three were born in Russia and in 1881 were living at 166 Camden Road, London.
Carl Hentschel was a photo-etcher, engraver and lithographer. He invented the Hetschell colourtype process, a revolution in newspaper illustration. JW knew him about 1898 (he spells the name 'Henschell'). He is said to be the original of the character named 'Harris' in Jerome's Three Men in a boat.
UK census 1881, from http://www.familysearch.org (accessed 2004); Kelly's London Postal Directory, London, 1893; 'Mr. Carl Hentschel', Times, London, 10 January 1930, p. 14.