Migrating user profile picture from D6 to D7
I believe you need to do picture migration separately per the docs (assuming you are using Migrate D2D, which you probably should).  This is all I had for picture migration from one I did last year:

$picture_arguments = $common_arguments + array(
  'machine_name' =&gt; 'pictures',
  'description' =&gt; t('Migration of user pictures from Drupal 6'),
  'default_uid' =&gt; 1,
  'source_dir' =&gt; '/some/path/to/sites/default/files/',
  'destination_dir' =&gt; 'public://pictures',
);

Migration::registerMigration('DrupalPicture6Migration', $picture_arguments['machine_name'], $picture_arguments);