The easiest and most honest method is to send a friend request. If they accept, you gain access to their public-facing photos according to their privacy settings. Look for Public Backups
Before we dive into the methods, it's essential to understand Facebook's privacy settings. When a user sets their profile photos to private, it means that only their approved friends or followers can view those photos. Facebook's privacy settings allow users to control who can see their content, including profile photos. facebook private profile photo viewer full