How could I do that for example via functions.php?

Now, I heard from Mark Jaquith you are not suppose to use kses for ouptputing stuff (performance wise). So if I need to output some user input html, how do I do that? I mean, how do I make sure I’m escaping right and letting that html pass through?

I’m trying to make a plugin for kses – basically I want to allow images, but I want to replace

<img src="x" /> with <a href="x"><img src="x" /></a></code>

So here’s where I am right now:

global $allowedtags;
$allowedtags['img'] = array( 'src' => array () );

//take images, and enclose them in a link
function zimgf($ztring){
$result = preg_replace('/<img src="(.+)"(.+)\/>/Ui', '<a href="$1"><img src="$1"$2/></a>', $ztring);
return $result;
}

add_filter('pre-kses', 'zimgf');

Problem is, while this does allow the images through, it doesn’t do the replacing part (the regex works, tried it separately).

wp_kses($unfiltered, ”) if i don’t want any html tags allowed?