This is not going to sound nice, but it is the truth. You only know a little of the truth at this point. Until your daughter is away from SS and feels safe and like she won't be forced to ever have to deal with him again, you will not know the full extent of what he did or how she feels. You know about the phone and the photos. You don't know if he ever forced her to let him take other photos, or to do other things. You don't know if he was just starting out to be a sexual predator, or if this was the straw that broke the camel's back.
Sometimes the pictures and the fear of having them on the internet are what breaks the hold on a victim. Sometimes taking photos the way SS has is just the beginning. Until your daughter knows she is away and safe from SS for good, and she is in therapy with someone she trusts, you won't know the extent of things.
You NEED to contact a domestic violence center in a neighboring county. NOT your county. It may be an hour drive or longer, but it will be worth it. Or you should contact RAINN, a nationwide sexual assault organization (RAINN | The nation's largest anti-sexual violence organization ) They can help you find resources that are far enough out of your relatives' influence that they will be effective and confidential.