You can try with
protected function create(array $data)
{
$user = User::create([
'email' => $data['email'],
'first_name' => $data['first_name'],
'last_name' => $data['last_name'],
'display_name' => $data['display_name'],
'title' => $data['title'],
'location' => $data['location'],
'work_phone' => $data['work_phone'],
'cell_phone' => $data['cell_phone'],
'skype' => $data['skype'],
'twitter' => $data['twitter'],
'password' => bcrypt($data['password']),
]);
// $user->id <--this is id
Image::make($data['profile_img']->getRealPath())->resize(128,128)->save(public_path('storage/avatars/' . /* User ID here */ . $data['profile_img']->extension()));
// Set User profile_img column in database as the user id .upload-extension
}