Possibly the same M10 seen in previous pictures is captured at the moment of firing its main armament. It has been apparently in the same location for a fair while, judging by the empty shell cases that have been discarded by the crew.
Probably the target is German infantry in a building, American doctorine and and possibly the crews sense of self preservation would have the TD pulling into cover after firing when engaging tanks, given the M10's weak armour.
http://en.wikipedia.org/wiki/M10_tank_destroyer