Hello Stig,
As ever wouldn't a date on the photo be nice
Having said that the easiest way to differentiate between a B.E.2c and a B.E.2d externally is said to be in the size of the much larger underwing gravity fuel tank, which checking my copy of J.M. Bruce The Aeroplanes of the Royal Flying Corps does appear to be the case. Therefore, I feel reasonably confident the plane in the photo is a B.E.2c.
Regards,
Clint