Go to gravatar.com and create what is known as an avatar. The email address you use to post comments here must be the same as the email address you use when you sign up for an avatar on Gravatar.
Gravatar, it is easy, free, quick and we are not aware of any problems with it. no spam, no identity issues, nothing. But it is a third party site.
You don’t HAVE to use that site, you can use whatever one you wish, you can Google “avatar” and choose.
And if you value your anonymity you don’t have to use your “actual” image either. Pick any photo that would look good in a small space.