HEre's the best read out there right now....

http://www.anu.edu.au/BoZo/Scott/PDF Files/2001.Keoghetal.P.curtus.pdf

Once you look at enough of them, you can start to really be able to distinguish between them.....some are tricky though.

There's also a nice side head comparison on the BloodPythons site.....

www.bloodpythons.com