We have no concept of public upload albums. I personally would not grant anyone I don't know upload rights at all.... Security you know.
The register_user plugin lets you set default rights to a user which can be only "upload" rights and to a specific user album. Otherwise you have to create a user group an assign those users.
You possibly could write a plugin to auto assign a user to a specific group. See the plugin tutorial for info about available filters. Also the object model tutorial might be of help.