Based on the new gallery island in V7.6.2 I use this code:
Code
/* PHP CODE HERE */
$query = "
	SELECT
		`POST_ID`, `FILE_DIR`, `FILE_NAME`
	FROM
		`{$config['TABLE_PREFIX']}FILES`
	WHERE
		`FILE_DIR`<>''
	ORDER BY
		rand()
	LIMIT
		1
";
$sth = $dbh->do_query($query,__LINE__,__FILE__);
list($postId,$fDir,$fName) = $dbh->fetch_array($sth);

/* BODY HERE */
$body = <<<EOF
<div class="p2" style="height:180px;overflow:hidden;position:relative;width:180px;display:inline-block;">
<a href="{$config['BASE_URL']}/ubbthreads.php?ubb=showgallery&Number=$postId">
<img src="{$config['BASE_URL']}/gallery/$fDir/medium/$fName" alt="" title="" class="p2 cp oi" style="position:absolute;left:-100%;right:-100%;top:-100%;bottom:-100%;margin:auto;min-height:100%;height:180px;">
</a>
</div>
EOF;
It use the medium picture for preview and crop it to a fill out the whole box.
Please note that this code scan the content of the directory on the server and display orphaned files and the threads too. This gives me a lot of work to do on my board.

my board: http://www.dragonclan-forum.de
my hobby: http://www.biker-reise.de
Ich kann bei Fragen zu UBBthreads in Deutsch weiterhelfen oder es zumindest versuchen