It's up to you how to do this, but printing it out and scanning it is impractical for a lot of reasons. It's going to mess up the size and possibly the alignment of some lines due to some rotation upon printing/scanning the picture. And why waste real ink when you can paint it in PS?

Having a tablet might make things easier.

"Stephen Wolfram is the creator of Mathematica and is widely regarded as the most important innovator in scientific and technical computing today." - Stephen Wolfram