Customize the login form in WordPress

customize-wp-login.php

<?php
/**
 * Customize the login form in WordPress
 * @author Micah Wood <micah@wpscholar.com>
 */

/**
 * Change the href for the logo link on login page to point to the main site
 */
add_filter( 'login_headerurl', 'change_login_headerurl' );
function change_login_headerurl(){ return home_url(); }

/**
 * Change the title attribute for the logo link on the login page to be the tagline
 */
add_filter('login_headertitle', 'change_login_headertitle');
function change_login_headertitle(){  return get_bloginfo('description'); }

/**
 * Add our custom css and background image to the header of the login page
 * Note: You will need to adjust the URL to point to a valid image file
 */
add_action('login_head', 'change_login_head');
function change_login_head(){ 
    echo '<style type="text/css">#login h1 a { background: url("../images/logo.png") no-repeat; }</style>'; 
}