In What smart ways to prevent "image rot" can we come up with?, sth wrote:
In August 2010 I fetched a copy of all images in posts on SO/SF/SU/META, based on the URLs found in the data dump (probably the one of July). [...] I still have all those images on disk, in case more are broken by now and somebody wants to start an effort to re-upload them somewhere or such.
If many users were using Stashbox, then maybe the team can somehow use this backup to upload them to Imgur after all?
If not, keep your fingers crossed that Stashbox lives up to their June post and then use the "from the web" option in the image upload dialog, to transfer a copy to Imgur:
[...] we may mirror it on Amazon S3 so that users can grab anything they care about before it's gone forever.
We're working on ways to distribute files back to their owners. Stay tuned...