I remember creating an X-Face[0] using Atkinson Dithering for my SeaMonkey add-on MessageFaces[1]!

You can create one online here[2], but it doesn't seem to support Atkinson for whatever reason.

[0]: https://en.wikipedia.org/wiki/X-Face

[1]: https://github.com/JohnDDuncanIII/messagefaces

[2]: https://www.dairiki.org/xface/