Allow anonymous users to post content but require login/register before it is saved
This module might be worth looking at as well: Create and Register. Below are some more details about this module, and how it works (summary from the module's project page).


  This module allows an anonymous user to create the content. After
  doing so the user must login (or registers to the site). Here are some
  more details about the process to do so:
  
  
  anonymous user creates a content.
  the user will be redirected to the login page (if you set it on the settings form) after the user finished the node creation.
  the user registers or logs in.
  the created node(s) will be assigned to the user after logging in.