There's a thread with pictures embedded in the comments [here](https://stacker.news/items/3065).

The following markdown snippet:

```
![flammarion](https://github.com/abetusk/2d/blob/release/3rdparty/Flammarion-color-1.jpg?raw=true)
```

Will produce:

![flammarion](https://github.com/abetusk/2d/blob/release/3rdparty/Flammarion-color-1.jpg?raw=true)

abetusk

This link has all the formatting options https://guides.github.com/features/mastering-markdown/