You can compare objects using == and ===.

<?php
  class some_class {
    public $var = 'foo';
  }
  $a = new some_class;
  $b = $a;
  $c = clone $a;
  $d = clone $a;
  $d->var = 'bar';

  var_dump($a==$b);  echo '<br />';
  var_dump($a===$b); echo '<br />';
  var_dump($a==$c);  echo '<br />';
  var_dump($a===$c); echo '<br />';
  var_dump($a==$d);  echo '<br />';
  var_dump($a===$d); echo '<br />';
?>
Output
bool(true)
bool(true)
bool(true)
bool(false)
bool(false)
bool(false)