At the top of the page, click the Settings tab.
On the left side of the page, click Privacy.
Select Enable avatars.
Under Service address, type the URL of your avatar host or leave the text field empty to use the default value of https://secure.gravatar.com.
Under Identicons host, choose either your local GitHub Enterprise appliance or GitHub.com. The identicons host must be accessible by the avatar service via HTTP or HTTPS.
At the bottom of the page, click Save settings.
Wait for the configuration run to complete.