Facebook won't allow you to hide your profile picture and cover photo (these will be always public, no matter what are you settings). The workaround is to simply change/blur the profile picture, create a fake profile (which isn't allowed) or deactivating your account for some period of time.
On Facebook Help Centre we can read:
Anyone can see your public information, which includes your name, profile picture, cover photo, gender, username, user ID (account number), and networks (learn why).
What information is public?
Information you share that is always public: Some of the information you give us when you fill out your profile is public, such as your age range, language and country. We also use a part of your profile, called your Public Profile, to help connect you with friends and family. Your Public Profile includes your name, gender, username and user ID (account number), profile picture, cover photo and networks. This info is also public. Some of the ways this helps us connect you are:
- Your name, profile picture and cover photo help people recognize you
- Gender helps us describe you (ex: "Add her as a friend")
- Listing your networks (ex: school, workplace) allows others to find you more easily
- Username and user ID (ex: your account number) are in the URL of your profile
- Age range helps provide you with age-appropriate content
- Language and country help us provide appropriate content and experiences