iOS -> Settings -> Privacy and Security -> Photos -> Facebook -> Set limited access
You'd have to block nearly every app from ever seeing any image you don't want Facebook getting ahold of including apps that are made by other companies. Almost everyone uses their libraries, they practically have a shell on your phone (which is funny because you're not allowed that on your own device for "security.")
However, I wish they’d grow a pair and just outright block the FB and other similar dependencies that make such stuff necessary.