Stephen C. Sweeney, I think

My aunt Gladys Brown gave me this photo. She was pretty sure it was her grandfather, Stephen Cassin Sweeney who was born in VA and lived in TN, MO, &

I am fascinated by the uniform. I would love to know what kind of uniform it is. Also, the picture is imprinted on glass with a black backing that is wearing off. What kind of picture type would this be?