Help on unwanted registrations

[Cyberwin]

I have a small plublic travelphotogallery for dutch speaking people: http://www.reisfotos.info/

Minimum twice a week I got new unwanted registrations to my gallery. The new user have to confirm their registration by email. They put links to pornographic sites in their userinformation and start placing comments with links to these site.

What I do:
I created a new usergroup for my regular users, they can still post comments. New users cannot do this.
I am notified by email when a new user registers and personally take a look at his userinfo. (the user is banned or deleted)


Is it possible that this is done by an automatic script? (I cannot imagine that a human puts time in this activity)
Are there webmasters that have the same problem?
Is there something else I can do?

Thanks for your reactions.

[Nibbler]

Enable 'Admin activation of registrations' in config and/or take measures about comment spam (search the board for kismet or captcha).

[AmerGarRes]

I have the exact same problem. Some of the links are really nasty. Just wondering if other users are seeing this kind of thing, too. Does it drop off eventually? I see that the usernames are all similar. Usually a name followed by four numerals.

I will check on the kismet and captcha suggestions.