changing the BBCode allowed (I am terribly sorry for double post, please delete)

[remp]

OK, so i have this function:

function BBCode($str) {
   
   //
   // Change this (BBCode)
   //
    $change = array(
                '/\[b\](.*?)\[\/b\]/is',                               
                '/\[i\](.*?)\[\/i\]/is',                               
                '/\[u\](.*?)\[\/u\]/is',                               
                '/\[url\=(.*?)\](.*?)\[\/url\]/is',                         
                '/\[url\](.*?)\[\/url\]/is',   
            '/\[img\=(.*?)\](.*?)\[\/img\]/is',   
                );

   //
   // With this (HTML)
   //
    $with = array(
                '<strong>$1</strong>',
                '<em>$1</em>',
                '<u>$1</u>',
                '<a href="$1">$2</a>',
                '<a href="$1">$1</a>',
                  
                );

    // Replace
    $str = preg_replace($change, $with, $str);

    return $str;
} 

which replaces the imput with actual code so users could post links, make it bold, italic and other stuff, this is commonly called the "BBCode allowed"

how can i change this so that users can also insert images?