Customize WordPress login logo without a plugin

WordPress login logo looks nice, but sometimes you may want to change it, for example when building a site for a client. In that case, you can use a plugin, or simply take advantage of this cool hack
Nothing hard with this recipe. The only thing you have to do is to copy the following piece of code, and paste it on your functions.php file:

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');