mrm_be/Configuration/TCA/Overrides/sys_file_reference.php

<?php
$lll = 'LLL:EXT:mrm_be/Resources/Private/Language/locallang_ttc.xlf:sys_file_metadata';

$columns = [
  'copyright' => [
      'l10n_mode' => 'prefixLangTitle',
      'exclude' => true,
      'label' => $lll.".column.copyright",
      'config' => [
          'type' => 'input',
          'size' => 20,
          'eval' => 'trim',
          'placeholder' => '__row|uid_local|metadata|copyright',
          'mode' => 'useOrOverridePlaceholder',
          'default' => null,
      ],
  ],
];

\TYPO3\CMS\Core\Utility\ExtensionManagementUtility::addTCAcolumns("sys_file_reference", $columns);

\TYPO3\CMS\Core\Utility\ExtensionManagementUtility::addFieldsToPalette(
    'sys_file_reference',
    'imageoverlayPalette',
    '--linebreak--, copyright'
);