Add a custom logo to the login screen for wordpress.

CustomLoginLogo.php

/**
 * Custom admin login header link
 */
function custom_login_url() {
    return home_url( '/' );
}
add_filter( 'login_headerurl', 'custom_login_url' );

/**
 * Custom admin login header link alt text
 */
function custom_login_title() {
    return get_option( 'blogname' );
}
add_filter( 'login_headertitle', 'custom_login_title' );