Websites that claim you can simply paste a profile URL to unlock private photos rely on deceptive tactics to exploit user curiosity. How the Scams Work
They simply find the low-resolution thumbnail that is already public and enlarge it (resulting in a blurry image).
: Many of these sites ask you to log in with your own Facebook credentials to "verify" you, which allows them to hijack your account.
That being said, here are some general points to consider:
If you genuinely need to see a profile picture, there are legal, non-malicious ways to go about it. None involve hacking, and all respect the user’s privacy.