I think so far this has only been mentioned in comments, like about preventing link rot. So:
What smart ways to prevent images from disappearing can we come up with? Like maybe: how could we prevent image rot by requesting (some) images at some regular interval, or how could we get all (existing and future) images into the SE provided pro account at imgur.com?
Editing posts to move images to imgur.com bumps the question onto the front page†.
When the blog's images were lost, some of you came up with some very smart solutions to get them back, even from the visitor's browser cache!
Some users explicitly want to host their images elsewhere, to be able to update them and manage them without having to change the URL in the post, or because it makes them feel "more in control" with the files. Also, some workplaces block imgur.com (like using Websense), making some want to use other image hosters.
Can we somehow tell if an image at imgur.com has been uploaded to the SE pro account, or to an unrelated (possibly free) account?Since May 2011, images uploaded to the SE pro account use the
i.stack.imgur.comdomain, which apparently is a commercial Imgur installation for the Stack Exchange network. Before that, the image URL did not reveal if images were uploaded to some free account or the SE account. But then, in June 2011, SE changed many existing URLs to use the new URLs, even for images that are not hosted on the SE account. That effectively means some non-SE images are no longer linked, and hence will not get any views any more, and will be gone after some months.
Does the SE pro account need a backup? Its TOS claims, of course: Imgur makes no guarantee of availability of service and reserves the right to change, withdraw, suspend, or discontinue [...]. (Remember Flickr accidentally deleted 4,000 images of a paid subscription, and officially did not provide a backup, nor any means to restore existing URLs? And one can use filmot.com as a proxy to Imgur, but that does not keep its own copies.) Images uploaded to
i.stack.imgur.comdo probably get backed up, as Waffles commented: Our main goal here is to have local backups of images you folk upload and dedicated servers.
tinypic.info (not .com) seems to have gone bad: The website at img5.tinypic.info appears to host malware – software that can hurt your computer or otherwise operate without your consent. And existing references to images (such as img5.tinypic.info/files/361e5z58gdhp3kt1ryr6.jpg) are now serving ads, no images. But luckily these are HTML, so not visible when embedded as an image.
Do we need to detect image rot as well? Detecting it might give us an idea if this is a problem? Detecting might be hard though: nowadays imgur.com throws a 404 Not Found (with an error image in the same response), but it used to send a 301 Moved Permanently result for that. Things are really difficult for image hosters that respond with 200 OK, like tinypic.com gets one a 302 Moved Temporarily followed by a 200 OK for the 404 image.
† Not necessarily a problem; related: Could we have the ability to mark a change as minor in questions or answers?