Wordpress get first image from post but exculde image if word found in img src

[pengume]

Hello I am new to php but understand sometimes 

I am trying to exclude some images from this function that I found by running a preg_match but it seems to never work was hoping someone here could help me out. If you need more explanation just ask. Well here is the code.

function catch_that_image() {
  global $post, $posts;
  $first_img = '';
  $new_img_tag = "";

  ob_start();
  ob_end_clean();
  $output = preg_match_all('/<img.+src=[\'"]([^\'"]+)[\'"].*>/i', $post->post_content, $matches);
  
  $first_img = $matches [1] [0];
  $check_img = preg_match('(pheedo|feedburner)',$first_img);

  if ($check_img == false) {
$new_img_tag = "<img src='http://www.searchforhealth.com/wp-content/uploads/2010/06/featured-default.gif' width='67px' class='alignleft' />";
}
else {
  $new_img_tag = "<img src='" .  $first_img . "' width='300px' class='alignleft' />";
  }
  if(empty($first_img)){ //Defines a default image with 0 width
  $new_img_tag = "<img src='http://www.searchforhealth.com/wp-content/uploads/2010/06/featured-default.gif' width='67px' class='alignleft' />";
  }

  else{
$new_img_tag = "<img src='" .  $first_img . "' width='300px' class='alignleft' />";
         
}

  return $new_img_tag;
  }

[ram4nd]

By excluding SOME images you mean what?