Create A Loop Of Images

wp-loop-images.php

function catch_that_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] [0];

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







<?php
if (have_posts()) :
    while (have_posts()) : the_post(); ?>
        <a href="<?php the_permalink();?>" title="<?php the_title(); ?>" class="img-loop">
        <img src="http://media.smashingmagazine.com/wp-content/uploads/images/wordpress-loop-hacks/<?php echo catch_that_image() ?>" alt="<?php the_title(); ?>" />
        </a>
    endwhile;
endif;
?>

http://wp.smashingmagazine.com/2009/05/13/10-custom-fields-hacks-for-wordpress/