Gravatar’s started around 2009 and are still used. Simply put a gravatar is a visual representation of a person and they can be a graphic or a photo. It’s really up to you and your own personal preference.
Gravatar stands for Globally Recognized Avatar. And the global is important because it will show your image or graphic on any sites participating in the gravatar program. So if you were to comment on two different websites, the sites would show your image the same across the internet.
To get your free gravatar, you can sign up at https://en.gravatar.com/ and register your email address. Here, you will be able to upload an image for that email address. You also will have the option to add more than one email address. You can choose a different photo or image for the different email address. Just select the email address to change and upload a new image or choose one that is already attached to your account.
After you have set up the accounts at the link above, you will notice in any of your WordPress sites that use the same email address the image in the profile will be the same. If you have set up your to use a forum or a member site, any members that have registered their emails will also have their image appear on your site. Another use would be to show the author image in your post – Similar to what I have done in the footer of this section. If you had multiple authors writing for your blog you can easily display their info at the bottom of their posts.
If a user has not set up a gravatar there will be a gray “mystery person” image that will appear similar to this. Of course, you can’t force anyone to register their username but I would recommend instructions showing them where to add an image.