rex_media::isImageType PHP Method

    public static function isImageType($extension)
    {
        return in_array($extension, self::getImageTypes());
    }

         if ($media_manager) {
             $thumbnail = '<img class="thumbnail" src="' . rex_url::backendController(['rex_media_type' => 'rex_mediapool_preview', 'rex_media_file' => $encoded_file_name]) . '" alt="' . $alt . '" title="' . $alt . '" />';
         }
     }
 }
 // ----- get file size
 $size = $file_size;
 $file_size = rex_formatter::bytes($size);
 if ($file_title == '') {
     $file_title = '[' . rex_i18n::msg('pool_file_notitle') . ']';
 }
 $file_title .= ' [' . $file_id . ']';
 // ----- opener
 $opener_link = '';
 if ($opener_input_field == 'TINYIMG') {
     if (rex_media::isImageType(rex_file::extension($file_name))) {
         $opener_link .= '<a class="btn btn-select" href="javascript:insertImage(\'$file_name\',\'' . $files->getValue('title') . '\')">' . rex_i18n::msg('pool_image_get') . '</a>';
     }
 } elseif ($opener_input_field == 'TINY') {
     $opener_link .= '<a class="btn btn-select" href="javascript:insertLink(\'' . $file_name . '\');"">' . rex_i18n::msg('pool_link_get') . '</a>';
 } elseif ($opener_input_field != '') {
     $opener_link = '<a class="btn btn-xs btn-select" href="javascript:selectMedia(\'' . $file_name . '\', \'' . addslashes(htmlspecialchars($files->getValue('title'))) . '\');">' . rex_i18n::msg('pool_file_get') . '</a>';
     if (substr($opener_input_field, 0, 14) == 'REX_MEDIALIST_') {
         $opener_link = '<a class="btn btn-xs btn-select" href="javascript:selectMedialist(\'' . $file_name . '\');">' . rex_i18n::msg('pool_file_get') . '</a>';
     }
 }
 $ilink = rex_url::currentBackendPage(array_merge(['file_id' => $file_id, 'rex_file_category' => $rex_file_category], $arg_url));
 $add_td = '<td></td>';
 if ($PERMALL) {
     $add_td = '<td><input type="checkbox" name="selectedmedia[]" value="' . $file_name . '" /></td>';
 }