Profile Picture is known as Avatar. The website recognizes profile pictures as an avatar in WordPress. Users and admins both can assign avatars for their Account.
Avatars are shown in comments if it is created by the user. And if it is used by Admin then it is showed in replies and authors sections.
All User roles can have their avatars in WordPress. There are so many popular plugins to create avatars for users. But Admin should use Gravatars to crate his avatar on the Website.
Gravatar is a more convenient way for a Website owner to showcase his profile. It assigns a unique profile picture to an email address so that every time that email address is in contact with the WordPress website then it will show that image as the profile. Users can also create their Gravatars.
To crate a gravatar, simply visit their official website and create an account with your email that you use in websites.