IIRC, a lot of these site require that you share a unique photo or video (something they don't have in their library already) as a condition of membership. Thi

IIRC, a lot of these site require that you share a unique photo or video (something they don't have in their library already) as a condition of membership. This ensures that only the most serious users even get a chance to view the forums. These communities would have a lot more producers in them than your run-of-the-mill CP imageboards, as they have to fulfill a barrier to entry that only a seasoned CP consumer or producer would be able to meet. So, once the FBI have control of the site, they can sort out all the lurkers who are consuming but not actively participating (probably uncommon, given that these sites also require you to remain active to keep your membership) and get damning information about people who are mass-distributing/selling and/or producing child pornography.