<?php $postimageurl = get_post_meta($post->ID, 'post-img', true);
if ($postimageurl) {
?>
      <a href="<?php the_permalink(); ?>" rel="bookmark"><img src="<?php echo $postimageurl; ?>" alt="Post Pic" width="200" height="200" /></a>
<?php } else { ?>
      <a href="<?php the_permalink(); ?>" rel="bookmark"><img src="<?php bloginfo('template_url'); ?>/images/wprecipes.gif" alt="Screenshot" width="200" height="200" /></a>
<?php } ?>