Currently, there is little biographical information about Brown on the Internet, though you might consider linking here and here. There's more about him in books dealing with illustrators such as Fred Taraba's fairly recent Masters of American Illustration.
It seems that Brownie (as he was known by his illustrator and other friends) was an early adopter of reference photographs. This was influenced by his slow, careful approach to creating what look to be quickly-done illustrations. (They appear quickly-done because he mostly worked in crayon, pencil and washes that seem less substantial than illustrations done using oil paints.)
What interests me is that he was good at capturing facial expressions and character. How much of this was the product of the photos he took and how much was conscious deviations from the photographic images? I am not aware of any surviving reference photos from the 1920s and 30s that can be compared to the finished works they were used for, so perhaps that matter can't be resolved. Given that Brownie was highly skilled, I'll assume he used his photos as the starting point and didn't copy them slavishly.
Brownie was good, successful, and popular socially. Still, I place him a fraction of a notch below the likes of F.R. Gruger and Henry Patrick Raleigh who used similar media in their illustration work.