You can use [extension by Eric] UserAdvManager for this
interesting features have this plugin, but not working as it should
I select :
Enable - Confirmation by admin (no confirmation key sent)
and the same happens when I register a new user immediately logs the gallery without approval from the administrator.
Do you have set "unvalidated" and "validated" user groups in your gallery ? "unvalidated" group does not have any permission to see albums on your gallery. And "validated" group does have full or limited (it's your own choice) permissions to see albums.
When a visitor registers, he is automatically set in the "unvalidated" group since the administrator validate his registration. When done, this user will be automatically unset from "unvalidated" group and set in "validated".
Of course, you can give any name you want for "validated" and "unvalidated" ;-)