class.upload.php is a powerful and mature PHP class to manage uploaded files, and manipulate images in many ways. The script is available under a GPL license.
more info about the class
In fact, this can be done after the upload, just using PHP'chmod() function.
But it also depends on the permissions that are set for PHP on your server, as well as the permissions on the directory.
I might include in the class a setting to chmod uploaded files, for for obvious security reason, it will default to 644.