Change the Wordpress Logo in wp-admin login page

User hook login_head

Example

function custom_login_logo() {
echo '<style type="text/css">
h1 a { background-image: url('/images/cutompath.png') !important; background-size:100% !important;width:100% !important;}

</style>';
}
add_action('login_head', 'custom_login_logo');