Wordpress: wrap first image with `div`

functions.php

<?php
function supergeil_wrap_first_img_with_div($content) {
  $pattern  = '/<img ([^>]+) \/>/';
  $replacement = '<div class="supergeil"><img $1 /></div>';
  return preg_replace( $pattern, $replacement, $content, 1 );
}
add_filter( 'the_content', 'supergeil_wrap_first_img_with_div' ); 
?>