function change_image_stuff($html) {
        global $post;
        $html = preg_replace('/(alt|title)=\"[^"]*"\s/','$1="'.$post->post_title.'" ', $html);
        return $html;
}

add_filter( 'post_thumbnail_html', 'change_image_stuff', 10 );
add_filter( 'image_send_to_editor', 'change_image_stuff', 10 );