Añadir atributo alt a múltiples imágenes en una web

while (have_posts()) : the_post();

    global $post;
    if ( preg_match_all('/<img (.+?)>/', the_content(), $matches) ) {
            foreach ($matches[1] as $match) {
                    foreach ( wp_kses_hair($match, array('http')) as $attr)
                        $img[$attr['name']] = $attr['value'];
                    echo $img['src'];
            }
    }

endwhile;