Adding profile picture

I’ve done some searching and most everything I come up with is for Gravatar or adding a custom avatar in the discussions section, allowing users to pick a different avatar.

If I have a small picture of myself (avatar sized) and I want to use that JUST for me (the admin), how would I go about doing that?

When I post a comment I’d like that image to show up instead of one of the stock avatars (gravatars)… and I don’t want other authors to be able to select my image for themselves either.

Thanks.