rand(<img src="nuoroda">); 

$i = array("pirmas kodas", "antras kodas", "trecias kodas");

echo $i[rand(0, count($i)-1)];

<?php

$advert = array(); 

  $advert[] = '<a href="#">Banner 1</a>';

  $advert[] = '<a href="#">Banner 2</a>';

  $advert[] = '<a href="#">Banner 3</a>';

shuffle($advert); 

echo $advert[0];

?>