How to add the User:Picture field on the account registration form?
You can use Register with Picture module.


  This module exposes the 'upload picture' element to the registration
  form. It also gives you the ability to set a picture as required in
  the module settings.
  
  Drupal 7 Instructions
  
  
  Install and enable the module
  Navigate to: Configuration -> Account Settings. (admin/config/people/accounts)
  Check Enable user pictures if it isn't checked already.
  Confirm Enable pictures on registration is checked.
  Use the Registration Picture Field Weight field to adjust the display order of the picture field on the registration form. It can be
  a negative or positive number.