The image next to your comment is known as an avatar.

To get an avatar, you must register (free) at Gravatar.com. Make sure that you use your real email address.

Now when you leave a comment, with this same email address, your avatar will automatically be added.

And not only will your avatar be added to comments on this blog, but to every blog that uses Gravatar, and there are thousands of them.

And as a last little fact; The Gravatar site is owned by Automattic, the same company behind WordPress.