wpdb in external script

Can anyone please point me to an example of the $wpdb class being used in an external script (not a plugin)? I have a php script I’ve written that creates a png image (called like <img src="foo.php?parameter=bar"/>) based on data in my wordpress database. I currently declare the database and password and such by hand in the php code, but would like to make it more universal so I can share it with others. Thanks.