preg_match help

[pengume]

Hello,

I am new to php and want to know if this code I am using is correct.

I am trying to use preg_match() to check if there is a certain word in a variable. If the word is found then I want to display a different image then if it is not found . the code I am using isn't working right now.

$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' />";
  }

[salathe]

How is it "not working"? Can you give us an example string which misbehaves?