Finally the below code I added to page.tpl.php to show different images at on page refresh.

In IE8 it is working fine. Howevr with firefox the image is not shownup. Any clue ?

The code is as below.

<?php
function endswith($string, $test)
{
$strlen1 = strlen($string);
$testlen = strlen($test);
if($strlen1 < $testlen)
  return FALSE;
$diff = $strlen1 - $testlen;
$strend = substr($string, $diff);
return ($strend == $test);
}
$dirimage = realpath('.\sites\all\themes\myzen\templates\himg');
$directory = opendir($dirimage);
$counter = 0;
while ( FALSE !== ($file = readdir( $directory )) )
{
if(endswith($file, "jpg"))
{
  $counter++;
  $files[] = $file;
}
}

$counter--;
$which = rand(0,$counter) ;
$imagepath = $dirimage . "\\" . $files[$which];
?>
<img src="<?php print $imagepath ?>" />