The software required is usually proprietary, such as Dolphin or QuickCeph. You need to purchase it as part of your imaging software program. I don't think there is a free or shareware ceph tracing program out there, but I may be wrong.
I recommend the pencil method listed above to start with. I still trace film cephs in my practice using a pencil and ceph tracing paper when I need to. For the most part I do the "sunshine analysis", which means I hold the film up to the light for a few seconds and go "hmmm...."