You can now use one of the new Halo 5: Guardians Gamerpic's on your Xbox live profile.
majornelson.com
"Just in time for the release of Halo 5: Guardians next week, we are adding a collection of Halo-themed images to the Xbox One gamerpic gallery including The Master Chief and Spartan Locke. These new images are starting to roll out over the coming days but may take some time to appear in all Xbox Live regions. To change your gamerpic, go to Settings, About Me, Customize profile, Change gamerpic (this may vary if you’re a Preview Program member with the New Xbox One Experience)."
Source: majornelson.com