For a conducting surface in yz plane and a q somewhere along the x
axis, solution is the same as if there was no plane and a charge of
-q at -x along the axis. Solution is then:
This can be generalized to 2 conducting surfaces at right angles. ... etc.
Method of images also works for spherical symmetry. Let sphere at
origin, grounded and charge q distance p outside of sphere. Then image
charge at q' at p' has a relationship: 
and 
. So 
. Can then calculate
a force: 