Indeed there is a way to backup contact pics originally synced from Facebook, and in all probability its most likely already cooked into whatever ROM you are currently using.
What is this program I speak of?? Microsoft's MyPhone Service.
People seem to undervalue this program that MS almost quietly rolled out. It will sync anything from contacts w/multiple numbers/adresses/e-mails to calendar entries, to your ringtones (from \My Documents\My Ringtones)