Images manually uploaded to Imgur are not displaying?
I thought that images uploaded to
i.stack.imgur.com are supposed to remain permanently, but it seems some of them are getting deleted. The server returns a PNG image saying "The image you are requesting does not exist or is no longer available."
See Mathematica: Transparent background with PNG for an example.
This might be the same issue as Imgur images are (re)disappearing again.
A while ago, something like this happened transiently, where navigating to
http://i.imgur.com/[SAME PATH] in the browser fixed the problem, so it was presumably a server-side cache issue. But that doesn't work for these images.