Technically, it is impossible for a third-party website to "unlock" a private photo due to Facebook's core architecture:
: The Facebook Profile Picture Guard adds a visual shield and prevents the "right-click to save" or "screenshot" functions on mobile devices. facebook locked profile picture viewer online verified
: This is the only way authorized by Facebook to view a locked profile's photos. Technically, it is impossible for a third-party website
: You may be forced to complete endless surveys that generate money for the scammer but never show you the photo. facebook locked profile picture viewer online verified
To ensure your own photos remain private and cannot be "viewed" by strangers, you should: Lock your Facebook profile | Facebook Help Center