Ok. You've got a couple options depending on how you're wanting to use the curve.
You can make a selection of the curve, using quickmask or channel operations, then move the selection somewhere else and fill/edge/whatever using it.
The other option is to use Photoshop's bezier path tools to match the curve, then move the path around to where you need the reference.
I'm assuming you're using Photoshop here. If not, the GIMP has these same features.