Recently I've been thinking alot about this whole age verification thing, and all I can ask is why go through all the trouble? Why not just include a restriction into the game under a new option PARENTAL CONTROLS. Kinda like the V chip in your tv. Put a password protection on it, and bingo, then its not LL fault for kids being in adult areas, its the parents, and if you offer different restrictions PG,M,ADULT, parents can filter what their children see in sl.
I mean when you figure adult porn websites think website blockers are enough, why can't LL? Its alot less problematic, alot cheaper, and alot easier on the consumer. If you want to, you could even release the URL for the adult server log in, and the parents can block the connection right through their current filtering.
Less is more in this case, you want a system that works. This has been proven by the fact that every school in america probably has a website filter. And one that isn't hard on the people that are actually using this service. Which authentication with passports, foreign contry ids, really may result in business lost.
Edit:
I just thought of a problem resulting from age verification, what is to stop people from getting a friend to authenticate it, or authenticating an account then selling it? As it says, all data from the age verification is deleted as soon as its processed. So how could you guard against this?