How to auto strip hyperlinks & images in wordpress post

Here is one idea to strip link- and image tags from the post content (before you save it) by using the edit_post_content filter and the wp_kses function:

add_filter( 'edit_post_content', 'my_edit_post_content', 10, 1 );
function my_edit_post_content( $content ) { 
    if (!current_user_can('manage_options')) { // only strip for non-admins
        global $allowedposttags;
        $mytags = $allowedposttags;
        unset($mytags['a']);               // don't allow links
        unset($mytags['img']);             // don't allow images
        $content = wp_kses($content, $mytags);
    }
    return $content;
}

where $allowedposttags is defined here:

http://core.trac.wordpress.org/browser/tags/3.5.1/wp-includes/kses.php#L48