How to make a different field value for different roles?

Question

Drupal

Good day.
Site on Drupal 7.
There is a field for uploading an image. I would like to allow registered users to upload 6 files, and anonymous users 2.
I found this code:
<?php
function mymodule_form_alter(&$form, &$form_state, $form_id) {
if ($form_id == 'name_node_form') {
array_unshift( $form['#validate'], 'addtonal_validate');
}
}
function addtonal_validate($form, $form_state {
$count = 0;
foreach($form_state['values']['field_img'] as $img) {
if (!empty($img['value'])) {
$count++;
}
}
global $user;
if (in_array('anonymous_user', $user->roles)) {
if ($count > 2) {
form_set_error('field_img', t('You cannot upload more than 2 img'));
}
}
}
?>
I insert it into my module, replace it with my own values, but nothing works. Tell me, maybe something is wrong in the code or there are other approaches?