[GRASSLIST:5736] image->vector

I've got an assigment to visualize one map with some data.
There are drawn districts on this map. Basically every district is a
polygon. I plan to scan this map and import it into grass as an image.

Question:
Does GRASS have ability to find out what those districts are? Or is
there posibility to tell it manually, for example by clicking on map -
following district borders?

I am just a beginner, happy for any help.
Thank you, Roman Varga