[MrNase]

Sure

I use the following code:

PHP Code:

                 // Thumbnails
              if($foruminfo['forumid'] == 22 AND $getpostid = $DB_site->query_first("
              SELECT postid FROM " . TABLE_PREFIX . "post WHERE threadid = $thread[threadid] LIMIT 1"))
              {
                  $attachment = $DB_site->query_first("
                  SELECT filename, attachmentid, IF(thumbnail_filesize > 0, 1, 0) AS hasthumbnail
                  FROM " . TABLE_PREFIX . "attachment
                  WHERE postid = $getpostid[postid]
                      ORDER BY rand() LIMIT 1
                      ");
                  $attachmentid = $attachment['attachmentid'];
                  $hasthumbnail = $attachment['hasthumbnail'];
                  }
                  // Thumbnails 


which reads out the attachmentids only from the images which have thumbnails. This excludes all txt or pdf or other files which are not images.
ORDER BY rand() LIMIT 1 tells him to output a randomly chosen attachment.

Together with the following conditional in the threadbit -Template it generates this beautiful gallery

     	<if condition="$show['threadicons']">
     		<td class="alt2">
     	<if condition="$foruminfo[forumid] == 22 AND $hasthumbnail">
     	<img src="attachment.php?attachmentid=$attachmentid&stc=1&thumb=1" /> <else />
 	<if condition="$show['threadicon']"><img src="$thread[threadiconpath]" alt="$thread[threadicontitle]" border="0" /><else />&nbsp;</if>
     	</if>
     	</if>

For some reasons this query doesn't work for any image and I couldn't find out why. But as most of the images work I don't care that much about it. Feel free to take my code and modify it