The Mason & Kelly photograph studio was located in Marshfield. Walter Mason came to Marshfield in 1889 and established the studio at 112 East Third Street. When Kelly joined the Mason firm I don't know. Mason died in 1909, and his studio was purchased between then and 1911 by the Stierle brothers, John and Joseph, who ran their photography studio from the former Mason site.
I checked the following indexes: I will put the most likely hits first.
Marriage Index , Wood County Marriages in Marriage Book I, 25 July 1867 to 30 October 1888.
Schaffer, Herman to Leonhard, Kate on 16 October 1888, Volume 1, page 69
Birth Index, as reported in the Marshfield News, prior to 1908
Schafer, baby girl, as reported on 14 November 1889, page 1, column 5. Notes: father Herman Shafer (surname spelling as recorded in the index)
Birth Index, as reported in the Marshfield Times, prior to 1908
Schafer, baby girl, as reported on 15 November 1889, page 1, column 8. Notes: to Mr and Mrs. Herman Shafer (again, surname spelling as recorded in the index)
Schaffer, baby girl, as reported on 19 Jun 1903, page 7, column 1. Notes: baby girl born to Mr. and Mrs. Joseph Schaffer at Fenwood., no date given.
Necrology Index, as reported in the Marshfield News prior to 1908
Schaffer, Gottfried, reported on 1 September 1898, page 5, column 3. Notes: Millworker, drowned-Little Eau Pleine River.
Schaffer, Theresin, reported on 22 July 1897, page 4, column 2. Notes: Died her home, city, left husband and two children.
Necrology Index, as reported in the Marshfield Times prior to 1908
Schaffer, William, reported 22 Nov 1901, page 7, column 3. Notes: of Merrillan/shot hunting near Boyd by William Kampf of Chippewa.
Schaffer, William, reported 22 November 1901, page 9, column 4. Notes: of Merrillan, funeral Alma Center, shot and killed while hunting.
Marriage Index, as reported in the Marshfield News, prior to 1908
Schaffer, Joseph, reported on 12 January 1899, page 9, column 4. Notes: of city, to wed Mrs. Mary Kelshoser of Sherry.
Schaffer, Joseph, reported on 19 January 1899, page 5, column 4. Notes: wed Mary Kelhoser; Rev Bruderman of Auburndale officiated.
Marriage Index, as reported in the Marshfield Times, prior to 1908
Schaffer, Bertha, reported on 21 March 1902, page 8, column 1. Notes: Both of town of McMillan, wed Henry Hahn.
1921 City Directory
No Herman Schaffer
Schaffer, William C. (Route 7) Route 7 was a south and east route from the city of Marshfield. My great-grandmother, who lived on Washington Avenue, was on Route 7)
Marshfield Cemetery Index
Gate of Heaven Cemetery, Section IV, Row 7
Schaffer, Anna 26 May 1849 - 7 Jan 1949
Schaffer, Casper 20 Mar 1855 - 7 July 1945
Gate of Heaven Cemetery, Section III, Row 7
Schaffer, Joseph 1858-1919
Schaffer, Theresia 1851-1897
I can check these indexes again for the Schafer or Schaefer name, but hesitate to just provide all of them here because of the number. Your help narrowing the search would be helpful if you are interested in any of these at all.