Random image in Smarty file

//php file
$smarty->assign('random', 
  array( 
    'photo1.jpg', 
    'photo2.jpg', 
    'photo3.jpg',
    'photo4.jpg'
  ));

//template file
<style>
{literal}
.myImageDiv {
background: url({/literal}{$siteurl}/themes/{$style}/styles/images/{$random.$randomimage}{literal}) no-repeat transparent;
height: 460px;
background-size: cover;
background-position: center;
}
{/literal}
</style>