I have an adult "swingers site" where I have various settings for my users privacy. One of them is that the site is closed to guest's.
I do however want guest's to sign up so I allow access to my forums and and bloggs for them.
I try to protect my members by blurring the avartars that appear next to their forum post's, blog post's and other places where their avatar might be visible to guest's.
The hope is that guest's will want to see the avatars unblurred and sign up. Its also unlikely a registerd member will be identified by anyone i.e family anf friends unless they themselves have signed up to the site.
Regular photo can still be viewed and cannot be blurred but in my case photo's are restricted to members only so they dont need to be.