Standard-Thumbnails für Kategorien From http://fastwp.de/snippets/standard-thumbnail-fuer-jede-kategorie/

wordpress-standard-thumbnails-kategorien.php

<?php
function default_category_featured_image()
	{
	global $post;
	$featured_image_exists = has_post_thumbnail($post->ID);
	if (!$featured_image_exists)
		{
		$attached_image = get_children("post_parent=$post->ID&post_type=attachment&post_mime_type=image&numberposts=1");
		if ($attached_image)
			{
			foreach($attached_image as $attachment_id => $attachment)
				{
				set_post_thumbnail($post->ID, $attachment);
				}
			}
		  else if (in_category('ID DER KATEGORIE 1'))
			{
			set_post_thumbnail($post->ID, 'BILD ID');
			}
		  else if (in_category('ID DER KATEGORIE 2'))
			{
			set_post_thumbnail($post->ID, 'BILD ID');
			}
		  else if (in_category('ID DER KATEGORIE 3'))
			{
			set_post_thumbnail($post->ID, 'BILD ID');
			}
		  else if (in_category('ID DER KATEGORIE 4'))
			{
			set_post_thumbnail($post->ID, 'BILD ID');
			}
		  else
			{
			set_post_thumbnail($post->ID, 'BILD ID FÜR ALLE ANDEREN FÄLLE');
			}
		}
	}
add_action('the_post', 'default_category_featured_image');
add_action('save_post', 'default_category_featured_image');
add_action('draft_to_publish', 'default_category_featured_image');
add_action('new_to_publish', 'default_category_featured_image');
add_action('pending_to_publish', 'default_category_featured_image');
add_action('future_to_publish', 'default_category_featured_image');
?>