I believe you can stil download any images from facebook. But probably won't be original size, most likely compressed version.I used signatures years ago but not anymore. It's not worth the effort. I never have seen someone who has stolen any of my pictures nor has anybody asked me about it. I mean I'm posting my pictures on FB, Insta, 500px and YouPic but then it's clear who's the owner. Apart from that I don't think that someone would steal FB pictures nor any copies from 500px or YouPic. Both platforms have download restrictions and so you can only make a snapshot of the picture which doesn't make sense at all.