How to get first image from post

Most WordPress users are using custom fields to display thumbs on their blog homepage. It is a good idea, but do you know that with a simple php function, you can grab the first image from the post, and display it.

to get you first image from the post just paste the below code in functions.php :

function first_image() {
  global $post, $posts;
  $first_img = '';
  ob_start();
  ob_end_clean();
  $output = preg_match_all('/<img.+src=[/'"]([^/'"]+)[/'"].*>/i', $post->post_content, $matches);
  $first_img = $matches[1];

  if(empty($first_img)){ //Defines a default image
    $first_img = "/images/default.jpg";
  }
  return $first_img;
}

once you have pasted the above code just , you can simply call the function within the loop to display the first image from the post: