Add the following code block in your themes’s function.php file and replace the image name and address (in bold text) with your own image.

function my_custom_login_logo() {

echo ‘<style type=”text/css”>

h1 a { background- image:url(‘.get_bloginfo(‘template_directory’).’/images/custom-login-logo.gif) !important; }

</style>’;

}

add_action(‘login_head’, ‘my_custom_login_logo’);