Photograph of a young man identified on the reverse as Elmer B. Lincoln, "Brother of Augusta". The photograph was taken by the J. E. Purdy & Co. studio of 145 Tremont Street, Boston, Massachusetts.
From brief online research, hopefully correct - corrections and additions requested:
Elmer Bertrand Lincoln, according to his Massachusetts Masons card, was born 26 July 1884 at Cambridge, Massachusetts, and died 16 April 1941. He was a chemist.
Elmer was the youngest child of Charles Sullivan Lincoln, a Civil War veteran, and second wife Celestna R. (Cook) Lincoln, who were natives of Eastport, Maine, and Perry, Maine, respectively. Among Elmer's siblings, including two older half-brothers, was sister Augusta Hobbs Lincoln, who married Charles L. Higgins in 1900.
In 1923 Elmer married Bertha Irene Lawrence, who was born in 1893 at Somerville, Massachusetts; they had at least one child, a son named after his father. Elmer and Bertha, who died in 1957 in Germany, are buried in the Forest Glen Cemetery at Reading, Massachusetts.
If you have corrections and/or additions to the information above, please leave a comment or contact me directly.