Problem mit Thumbnails bei Theme

<?php get_header(); ?>
 
<!-- BEGIN content -->
<div id="content">
 
 <!-- begin featured news -->
 <div class="featured">
 <h2>Featured News</h2>
 <div id="featured">
  <?php
  $tmp_query = $wp_query;
  query_posts('showposts=3&cat=' . get_cat_ID(dp_settings('featured')));
  if (have_posts()) :
  while (have_posts()) : the_post(); 
  ?>
  <!-- begin post -->
  <div class="fpost">
   <a href="<?php the_permalink(); ?>"><?php dp_attachment_image($post->ID, 'thumbnail', 'alt="' . $post->post_title . '"'); ?></a>
   <h3><a href="<?php the_permalink(); ?>"><?php the_title(); ?></a></h3>
   <p class="details"></p>
   <p><?php echo dp_clean($post->post_content, 300); ?></p>
  </div>
  <!-- end post -->
  <?php endwhile; endif; ?>
 </div>
 </div>
 <!-- end featured news -->
 
 <?php
 $wp_query = $tmp_query;
 if (have_posts()) :
 $odd = false;
 while (have_posts()) : the_post();
 $odd = !$odd;
 ?>
 
 <!-- begin post -->
 <div class="<?php if ($odd) echo 'uneven '; ?>post">
 <h3><a href="<?php the_permalink(); ?>"><?php the_title(); ?></a></h3>
 <a href="<?php the_permalink(); ?>"></a>
    <?php $screen = get_post_meta($post->ID,'screen', true); ?>
   <img src="<?php echo ($screen); ?>" width="181" height="100" alt=""  />
 <p><?php echo dp_clean($post->post_content, 150); ?></p>
 <div class="postmeta">
    <p class="category"><?php the_category(', '); ?></p>
 </div>
    </div>
 <!-- end post -->
 
 <?php endwhile; ?>
 
  <div class="postnav">
  <div class="navigation">
   <div class="alignleft"><?php next_posts_link('&laquo; Ältere Einträge') ?></div>
   <div class="alignright"><?php previous_posts_link('Neuere Einträge &raquo;') ?></div>
  </div>
  </div>
 
 <?php else : ?>
 <div class="notfound">
 <h2>Not Found</h2>
 <p>Sorry, but you are looking for something that is not here.</p>
 </div>
 <?php endif; ?>
 
</div>
<!-- END content -->
 
<?php get_sidebar(); get_footer(); ?>

<?php get_header(); ?>
 
<!-- BEGIN content -->
<div id="content">
 
 <?php $post = $posts[0]; // Hack. Set $post so that the_date() works. ?>
 <?php /* If this is a category archive */ if (is_category()) { ?>
 <h2 class="title">Archive for the <strong><?php single_cat_title(); ?></strong> Category</h2>
 <?php /* If this is a tag archive */ } elseif( is_tag() ) { ?>
 <h2 class="title">Posts Tagged <strong><?php single_tag_title(); ?></strong></h2>
 <?php /* If this is a daily archive */ } elseif (is_day()) { ?>
 <h2 class="title">Archive for <?php the_time('F jS, Y'); ?></h2>
 <?php /* If this is a monthly archive */ } elseif (is_month()) { ?>
 <h2 class="title">Archive for <?php the_time('F, Y'); ?></h2>
 <?php /* If this is a yearly archive */ } elseif (is_year()) { ?>
 <h2 class="title">Archive for <?php the_time('Y'); ?></h2>
 <?php /* If this is an author archive */ } elseif (is_author()) { ?>
 <h2 class="title">Author Archive</h2>
 <?php /* If this is a paged archive */ } elseif (isset($_GET['paged']) && !empty($_GET['paged'])) { ?>
 <h2 class="title">Blog Archives</h2>
 <?php } ?>
 
 <?php
 if (have_posts()) :
 $odd = false;
 while (have_posts()) : the_post();
 $odd = !$odd;
 ?>
 
 <!-- begin post -->
 <div class="<?php if ($odd) echo 'uneven '; ?>post">
 <h3><a href="<?php the_permalink(); ?>"><?php the_title(); ?></a></h3>
 <a href="<?php the_permalink(); ?>"><?php dp_attachment_image($post->ID, 'thumbnail', 'alt="' . $post->post_title . '"'); ?></a>
 <p><?php echo dp_clean($post->post_content, 150); ?></p>
 <p class="category"><?php the_category(', '); ?></p>
 <p class="comments"><?php comments_popup_link('No Comments', '1 Comment', '% Comments'); ?></p>
 </div>
 <!-- end post -->
 
 <?php endwhile; ?>
 
  <div class="postnav">
  <?php if(function_exists('wp_page_numbers')) { wp_page_numbers(); } ?>
  </div>
 
 <?php else : ?>
 <div class="notfound">
 <h2>Not Found</h2>
 <p>Sorry, but you are looking for something that is not here.</p>
 </div>
 <?php endif; ?>
 
</div>
<!-- END content -->
 
<?php get_sidebar(); get_footer(); ?>

<?php
include("settings.php");
# WIDGET: Sidebar
 
# WIDGET: Left Sidebar
if ( function_exists('register_sidebar') )
    register_sidebar(array(
  'name' => 'Left Sidebar',
        'before_title' => '<h2>',
        'after_title' => '</h2>',
  'before_widget' => '',
        'after_widget' => '',
    ));
 
# WIDGET: Right Sidebar
if ( function_exists('register_sidebar') )
    register_sidebar(array(
  'name' => 'Right Sidebar',
        'before_title' => '<h2>',
        'after_title' => '</h2>',
  'before_widget' => '',
        'after_widget' => '',
    ));
# Displays a list of pages
function dp_list_pages() {
 global $wpdb;
 $querystr = "SELECT $wpdb->posts.ID, $wpdb->posts.post_title FROM $wpdb->posts WHERE $wpdb->posts.post_status = 'publish' AND $wpdb->posts.post_type = 'page' ORDER BY $wpdb->posts.post_title ASC";
 $pageposts = $wpdb->get_results($querystr, OBJECT);
 if ($pageposts) {
  foreach ($pageposts as $post) {
   ?><li><a href="<?php echo get_permalink($post->ID); ?>"><?php echo $post->post_title; ?></a></li><?php 
  }
 }
}
# Displays a list of categories
function dp_list_categories($num=0, $exclude='') {
 if (strlen($exclude)>0) $exclude = '&exclude=' . $exclude;
 $categories = get_categories('hide_empty=1'.$exclude);
 $first = true; $count = 0;
 foreach ($categories as $category) {
  if ($num>0) { $count++; if ($count>$num) break; } // limit
  if ($category->parent<1) {
   if ($first) { $first = false; $f = ' class="f"'; } else { $f = ''; }
   ?><li<?php echo $f; ?>>
   <a href="<?php echo get_category_link($category->cat_ID); ?>"><?php echo $category->name ?><?php echo $raquo; ?></a></li>
   <?php
  }
 }
}
# Displays a list of popular posts
function dp_popular_posts($num, $pre='<li>', $suf='</li>', $excerpt=true) {
 global $wpdb;
 $querystr = "SELECT $wpdb->posts.post_title, $wpdb->posts.ID, $wpdb->posts.post_content FROM $wpdb->posts WHERE $wpdb->posts.post_status = 'publish' AND $wpdb->posts.post_type = 'post' ORDER BY $wpdb->posts.comment_count DESC LIMIT $num";
 $myposts = $wpdb->get_results($querystr, OBJECT);
 foreach($myposts as $post) {
  echo $pre;
  ?><a href="<?php echo get_permalink($post->ID); ?>"><?php echo $post->post_title ?></a><?php
  if ($excerpt) {
   ?><p><?php echo dp_clean($post->post_content, 120); ?>...</p><?php
  }
  echo $suf;
 }
}
# Displays a list of recent categories
function dp_recent_comments($num, $pre='<li>', $suf='</li>') {
 global $wpdb, $post;
 $querystr = "SELECT $wpdb->comments.comment_ID, $wpdb->comments.comment_post_ID, $wpdb->comments.comment_author, $wpdb->comments.comment_content, $wpdb->comments.comment_author_email FROM $wpdb->comments WHERE $wpdb->comments.comment_approved=1 ORDER BY $wpdb->comments.comment_date DESC LIMIT $num";
 $recentcomments = $wpdb->get_results($querystr, OBJECT);
 foreach ($recentcomments as $rc) {
  $post = get_post($rc->comment_post_ID);
  echo $pre;
  ?><strong><a href="<?php the_permalink() ?>#comment-<?php echo $rc->comment_ID ?>"><?php echo $rc->comment_author ?></a></strong> on <a href="<?php the_permalink() ?>#comment-<?php echo $rc->comment_ID ?>"><?php echo $post->post_title; ?></a><?php
  echo $suf;
 }
}
 
# Displays post image attachment (sizes: thumbnail, medium, full)
function dp_attachment_image($postid=0, $size='thumbnail', $attributes='') {
 if ($postid<1) $postid = get_the_ID();
 if ($images = get_children(array(
  'post_parent' => $postid,
  'post_type' => 'attachment',
  'numberposts' => 1,
  'post_mime_type' => 'image',)))
  foreach($images as $image) {
   $attachment=wp_get_attachment_image_src($image->ID, $size);
   ?><img src="<?php echo $attachment[0]; ?>" <?php echo $attributes; ?> /><?php
  }
}
# Removes tags and trailing dots from excerpt
function dp_clean($excerpt, $substr=0) {
 $string = strip_tags(str_replace('[...]', '...', $excerpt));
 if ($substr>0) {
  $string = substr($string, 0, $substr);
 }
 return $string;
}
# Displays the comment authors gravatar if available
function dp_gravatar($size=50, $attributes='', $author_email='') {
 global $comment, $settings;
 if (dp_settings('gravatar')=='enabled') {
  if (empty($author_email)) {
   ob_start();
   comment_author_email();
   $author_email = ob_get_clean();
  }
  $gravatar_url = 'http://www.gravatar.com/avatar/' . md5(strtolower($author_email)) . '?s=' . $size . '&amp;d=' . dp_settings('gravatar_fallback');
  ?><img src="<?php echo $gravatar_url; ?>" <?php echo $attributes ?>/><?php
 }
}
# Retrieves the setting's value depending on 'key'.
function dp_settings($key) {
 global $settings;
 return $settings[$key];
}
?>