Basically they have to request it.
What they don’t understand is that once their stuff is posted on the internet it’s out there. Requesting it to be removed from this forum is not going to limit the content available online and make someone want to pay to subscribe.
If people like what they see, they will subscribe regardless how much free content gets posted.
Requesting to be on the do not post list could actually hurt more than what the perceived benefits are due to less exposure.
If a girl is worried about her pictures being stolen or used without permission, then watermark everything with a custom domain name.