Take a look at this post (2 last links) http://moi3d.com/forum/index.php?webtag=MOI&msg=510.2 (not my Gallery of course :D

Draw from an "image" or a "photo" is always something hard because you can zoom the image!
So rounding of original form on the photo is not "precise" :)
Best is use Blueprints like this one :)
http://www.the-blueprints.com/

depend that you want of course :)