Follow below steps to change the login image and tooltip of the wordpress.
for this hack, you will require following Two files :
in wp-login.php page search for the “powered by” and replace that tooltip as per your convenience / requirement.
Now open login.css and search for the logo image. normally its in tag h1 a.
So you can change image like :
where “ShivaLogo.png” is your new image name.