Pvt. James Monroe Callaway, Company G, "Barksdale Grays," 20th Mississippi Infantry.
Pvt. James R. Wallace, Company D, "Fort Donelson Avengers," 35th Mississippi Infantry. He was mortally wounded at Vicksburg and died June 15, 1863.
Found both these images on Pinterest, no other info. Both Company G of the 20th and Company D of the 35th were from Winston County, Mississippi. Both images were obviously taken early in the war and they are wearing identical uniforms despite being in different companies and regiments, the 35th not organized until March 1862. Also same musket, bowie knife and pistol, though possibly photographer's props. Same poses. Same cases. Obviously both images were from the same studio. The large black hat pinned up with star on the side was typical for Mississippi troops early in the war; a lot of similar styles seen with Texas troops.
I wonder if James R. Wallace was originally in Company G of the 20th Mississippi when he had his photo taken and later transferred to or reenlisted in Company D of the 35th, hence the identical uniforms?