This would be a great addition for Piwigo or Community plug-in for photoalbums/sites that are mainly filled with user content.
The main thought: when you give a group access to a category (that is private) there would have to be an option to also give access to all child categories. Because now when a user adds a new album to a private category the admin first has to authorize the album for the other users in that group before they can see the album. This isn't really ideal when your photoalbum is mainly user driven.
Request following from this topic and more info: http://piwigo.org/forum/viewtopic.php?p … 47#p124247