You also might search for the phrase "Raster to vector" for some more information, here are some links:

http://en.wikipedia.org/wiki/Raster_to_vector
http://graphicssoft.about.com/od/bitmaptovector/Bitmap_to_Vector_Conversion_Tracing_Software_Raster_to_Vector.htm

http://wiki.inkscape.org/wiki/index.php/Tools#Vectorize.2Ftrace

I'd say probably try Inkscape at first...

- Michael