The original caption of this photo described the subject as an Estonian volunteer in German service, armed with a Solothurn S-18-100 anti-tank rifle. Another post shows a colorized version of what I believe is the same photo ( http://www.ww2incolor.com/hungary/345-Solothurn20mmmagyarcolor.html ), but identifies the subject as a Hungarian soldier. Given that the colorized uniform of the soldier is highly unusual for Hungarian army, I suspect this caption may be the more accurate one - but I don't really know.

Estonian Volunteer in German Service with ATR