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Something I've always wondered about these shields... How do you ensure the platforms where users embed them don't cache the images in their CDNs?

Is it just a matter of setting headers?

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If you load http://example.com and the HTML there includes an image tag that says '<img src="http://othersite.com/image.jpg">' it means your browser will connect to othersite.com and ask that site for the image. It will not ask example.com.

I'm asking about what happens when, for example, you embed a dynamic SVG badge in your GitHub readme.

Doesn't GitHub cache every image in their own CDN for security and control purposes?

You can't use <object>, <iframe> etc tags to embed pictures in your Github README, so you don't get automatic updates there no matter what (i.e. images would only refresh on page load). I don't know if Github proxies and caches <img> contents, or how long they cache it for but I haven't personally seen any delays when I've updated images used in READMEs.

But to repeat: auto-updating will not work for Github-hosted content AFAIK.

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