Just a simple but important hint today: If your user profile picture images are suddenly gone mysteriously, you should check your calls to user_save in custom modules or contributed modules.
The reason can be found in this Core issue: https://www.drupal.org/node/935592
You HAVE TO user_load() the full user object before user_save() it again, otherwise profile values are being reset.
This is quite dangerous, but logically okay. So take care!
