Several ways you could do it. The easiest is to assume your camera is fixed in position - not moving around. Then just define coordinates, templates, in a circle around the needle pivot point, and see which pixel is dark. Then use a look up table to turn that location into a dial reading.
If your camera moves around, so the dials are in different locations all the time, you'd have to use a different strategy but it would probably be better to just try to get your camera to not move around.
