SupeR-InG,
if (file_exists('../files/users/photo/' . $user['id'] . '_small.jpg')) {
echo '<a href="../files/users/photo/' . $user['id'] . '.jpg"><img src="../files/users/photo/' . $user['id'] . '_small.jpg" alt="' . htmlspecialchars($user['name']) . '" border="0" /></a><br/>';
}