Make it possible for your visitors to register. The registration can be enabled for the whole account, for specific categories, or for specific albums only. The registration can be mandatory or optional and the registration form consists of a heading and a message.
Set everything up quickly with setting inheritance. You can set the visitor registration form display mode by going to "Customize" >> "Site Settings" >> "Visitor Registration". By default, this setting is inherited to categories, and from categories to albums. If you wish to set things up differently for an album or a category (and let the setting be inherited from there), you can do so by going to "Tools" >> "Album / Category Settings" >> "Visitor Registration".
Think twice before making a registration mandatory. Most visitors are not very happy with filling forms and are likely to leave your site quickly. However, noone knows your visitors better than you do.
Optional registration can be skipped by using the "No, thanks" button.
If you feel that displaying a form before accessing the actual content can scare your visitors away, you can just keep a registration link in your menu, or link your registration form from your own site or blog as a supplemental registration option. You can find your registration form URL by going to "Customize" >> "Site Settings" >> "Visitor Registration" at the top.
You can ask them any three questions you can come up with. You can also request any of the following : name, e-mail, phone number. Each of the fields can be required, optional, or hidden. You can also set up notifications so that you receive an e-mail every time someone registers with your account and you can have their e-mails automatically added to your BlueMelon contact list.
Once someone has registered, you can view their activity at the "My Stuff" >> "Visitor Registrations" page. On this page, you can see all of your registered visitors, their details, and the photos that they have marked as "liked". You can also add visitors' e-mail addresses to your contact list or remove registrations.