Github allows you to embed images in a wiki page.
The problem seems to be that for private repos, the right to access the image is determined by a transient token appended to the URL like this:
https://media.githubusercontent.com/media/XYZ/MyProject/master/WikiMedia/Foo.png?token=XXXXXXXXXX-YYYYYYYYYYYYYYY-YYYYYYYYYYYYYYY
This URL work but only transiently; is there a more stable way?