- htmlentities: documentation ( source)
- preg_replace: documentation ( source)
<?php
$string = 'HDO Intranet — Futar.png';
$encoded = htmlentities($string);
$result = $encoded;
$result = preg_replace('/&([a-z]{1,2})(?:acute|cedil|circ|grave|lig|orn|ring|slash|tilde|uml);/i', '$1', $result);
$result = preg_replace('/&([a-z]{1,2})[a-z]+;/i', '$1', $result);
$result = preg_replace('/[^a-zA-Z\d\s-_\.;&]/', '', $result);
echo $result;