Several websites specialize in this service. Generally, the process is:
Viewers locate the specific image ID in the page link. fb profile picture viewer
There are several unofficial browser extensions and websites designed to help you view a full-sized or "locked" profile picture that you otherwise wouldn't be able to click on. Several websites specialize in this service
It is important to understand the limitations and potential risks of using these tools. fb profile picture viewer
Many tools work without requiring you to log in to your own account. How to View a Full-Size Facebook Profile Picture