In class on Tuesday (11/13) I said that once a vector
  image has been rastorized, there is no good way to get
  back to the vector representation.

  Today I found out about a free web site that will
  vectorize bitmaps. If you are interested, it's at:
  http://vectormagic.stanford.edu
  You can upload any type of image (jpeg, gif, png),
  and it lets you download an svg (scalable vector graphics)
  file. There is a short video tutorial on the home page to
  help you get started if you want to play with it.
  
  Unfortunately, Fireworks doesn't know how to work
  with svg files. In the lab, however, you could open the
  svg file using Inkscape. If you have Adobe Illustrator,
  that can open svg files directly. And firefox can display
  them, too. (Drag an svg file onto a firefox window, and it
  displays the picture.)

  Dr. Vickery