This just isn't true. If I post a photo on Facebook, I license Facebook to use that image in some ways (ie posting the photo in people's newsfeeds, possibly using it in ads, etc). However, I still own the copyright in that image. If someone else posts that image elsewhere, I can make them take it down or sue them. The images are most definitely not in the public domain in any legal sense.
Moreover, who cares? It's fucking creepy to take someone's photos off their personal page and post them on a site like this. It's even worse when it's done associated with their real name. Camcaps should ban any posts like this and ban any user who does it.