[layer8]

This is nonsense. The actual file at the URL could change at any time. No system is doing something like that if it isn’t serving the file itself.

And, getting back to the original point, you wouldn’t be worrying that GitHub doesn’t “support” a URL that happens to point to a file of a particular subformat that the URL itself doesn’t disclose.

[Evidlo]

Doesn't Github already replace externally linked images with its own cached version when rendering out Markdown files?

[shepherdjerred]

GitHub definitely mirrors images. Any image you see on a README will be loaded from githubusercontent.com