CodePen avatars default to Gravatar. Gravatar associates an avatar with your email address. If you have a (free) Gravatar account, the Gravatar image you associate with the email in your CodePen profile will automatically become your avatar here on CodePen.
If you prefer to use something different on CodePen, you can change your avatar on the “Profile” tab in your Settings.
Click “Choose File” next to your current avatar image to upload a new one from your device. Ideal avatar dimensions are 500px x 500px. Maximum file size is 5mb.