GitHub uses "camo" (anonymized image URLs) for all external images that appears on GitHub, like when rendered in a README file, in a document, or in issues/pull requests. Using a proxy for images provides several benefits:
Performance: Less traffic through the image server - for popular images the "camo" cache does its job almost all the time.
Functionality: What if the origin server is misconfigured and makes a small (but critical) mistake in, for example, handling CORS?
Durability: The origin server is down - okay, the "camo" cache is available for serving.
Worse, what if the image is later changed on the server (under the same URL) to something else? Best they tell you they're not hosting your images, or just replace your image with terrible ads they can make 💰💰💰 out of. This is not unprecedented.
Privacy: The image server can't track users directly, or even get to know how many visitors there are.
That said, a "camo" service is going to be beneficial all the way, but SE is still linking to whatever images directly.
Since SE is already using Imgur for image hosting, why not just detect all external images, and before the post is submitted, automatically fetch and store them onto Imgur? This will directly address the following issues:
