another free service, just paste :

Code:
	  <%if $url!='http://' %><img src="http://www.thumbalizr.com/api/?url=<%$url%>&width=250" border="0" alt="<%$title%>" width="234" rel="nofollow"><%/if%>
where you want the code. You can use it as a backup to your own thumbnails by doing an if statment. ( if $screenshot|smartyexist )