The dark luminosity value in the original B/W, but then again, he could've been cavalry. I ruled out infantry more or less because it wasn't as bright as I'd expect a blue stripe/rank to be, and he's only holding a pistol, not an Enfield or anything along those lines. I imagine, if he was an infantrist, he would've been wanting to hold even just a studio prop to show off, really - also because I really like the way the red color looks. Artistic license I guess you can call it.
Oh, and the others I download off of the Liljenquist collection all have the rank stripes and leg stripes colored in artificially by the photographer/a third person, this one didn't - quite peculiar.