I think it's not that easy for Facebook to steal images that were uploaded by people NOT AUTHORIZED to cede rights to Facebook.
If a model gets images after a portfolio/test shoot, she usually gets self-promotion rights. But she cannot give anybody else any rights. If she uploads the images to Facebook, Facebook cannot just say: "It is on our turf, we can do what we want with it".
Copyright is a right, and rights cannot be so easily forfeited. If you own a parking lot and put up a sign: "You park here, your car is mine" it's still not legal, and if you tow and sell a car parked there it is still theft.
If it were true that you could lose rights so easily, all Facebook has to do is: charge a Facebook worker to go to your website, steal the image, and upload it to Facebook. And there they have free images for campaigns.
If Facebook did that, there would be a storm of anger, and will damage Facebook's stock.
Still, I no longer upload my work to Facebook.
Facebook, as a marketing too, is worthless anyway, except if you are doing weddings or family portraits.
I will have models sign a paper where they promise not to upload to Facebook.
It's in the model's interest as well. Which model wants to show up in an ad on Facebook in a before/after picture or in an ad that reads: "If got herpes and more - and I've got the Ivy Creme".
Not sure if Facebook will be around in ten years anyway. It's basically a big collection of chatter without any noticeable content.
Another thougth: if you buy stolen goods, you are still liable for "acquiring stolen goods" and can go to jail. Facebook cannot just push the blame onto the thief. Particularly as it is well known that a large number of images uploaded to Facebook are stolen.