It is difficult to believe but there were at least three people in eastern US, in the 19th century, named DeWitt Clinton Pratt; a constable, a carpenter and a photographer. There were even more named DeWitt Pratt, D. Pratt and D. C. Pratt.
D. C. Pratt spent most of his career working in Aurora, IL. When he died in 1903 his son, Edmund carried on the profession with a few interruptions until his death in 1924.
The timeline here shows a few variances in the studio address which should help date a card when the address is included in imprint.
DeWitt Clinton Pratt
(1823 - 1903)
Births of children included in lieu of other unavailable documents to show the location of D. C. Pratt
1823 Aug 14
D. C. Pratt born in Homer, Cortland, NY
1847 Jul 13
marries Mary M Burdick
daughter Florence Mary Pratt born in Aurora, IL
1856 Feb 14
daughter Eveline Estelle Pratt born in Lake Forest, IL
daughter Francis Eugenia Pratt born in Aurora, IL
1860 Jun 14
US census as “Artist” in Aurora, IL
1863 Jul 01
Civil War draft registration, as artist
Aurora, IL, city directory as photographer
1866 Oct 16
son Edmund C. Pratt born in Aurora, IL
Aurora, IL, city directory as photographer at 48 Broadway
1870 Jul 20
US census as photographer
1880 Jun 12
US census as photographer at 48 s Broadway
marries Charlotte A. Pratt in Aurora, IL
1900 Jun 01
US census as photographer; res at 19 so Lincoln
Aurora, IL, city directory as photographer; res 19 so Lincoln
1903 Aug 24
dies in Aurora, IL at age 80
So DeWitt Clinton Pratt was an active photographer from about 1850 to 1902. From the physical appearance of the card, it was probably done early in the decade following 1890.