The Display picture or Profile picture is your basic identification on social media handles, and thus it is very important to keep it secure, especially if you have a public profile. Anyone can ...

When you lock your profile, only your Facebook friends can see the content on your timeline. The full-size version of your profile picture and cover photo is also only visible to your friends.

Once you lock your Facebook profile, non-friends will not be able to zoom into, share or download your full-size profile picture and cover photo. The feature is aimed particularly at women.