I found that the "best" way is to use HTML, as it works both in Readme/.md files and also in comments (within Issues, Gist...)
E.g. when adding/editing a comment (within Issues, Gist...) :
- Upload the picture by drag-and-drop in the text field
- replace
![image](https://your-image-url.type)
with<img src="https://your-image-url.type" width="100" height="100">
As mentioned by @cbestow (thanks!), it's not mandatory to set both width
and height
. If only one is set, the other will be adjusted accordingly to preserve the aspect ratio of the image.