For at least the past 20 hours, https://i.stack.imgur.com/zOc0U.jpg as used in a question on Meta Stack Overflow shows a generated image claiming "The image you are requesting does not exist or is no longer available". Like:
GET /zOc0U.jpg HTTP/1.1 Host: i.imgur.com HTTP/1.1 301 Moved Permanently Content-Type: image/png Content-Length: 2609 Expires: Mon, 16 Jan 2012 10:50:29 GMT Cache-Control: max-age=31536000
The author meanwhile has indicated he used the upload feature from the editor.
Note that after refreshing a page, Safari might not show the generated image either, eventually timing out. A copy of the generated image, just for future reference if this is ever fixed:
(My Safari on a Mac times out after a refresh. That could be caused by the missing
Location in the HTTP
301 Moved Permanently; using Chrome or Firefox always seems to get me the generated image. I am not sure if the missing
Location is an Imgur feature, but that's not the issue here. I have not tested the refresh with Internet Explorer.)