I've just noticed on some questions like this one there is an "image not found" link for imgur. I think it used to be an icon for the Ubuntu package manager.
At first I thought these were added automatically on any link to the package manager, but it looks like the user Sid has edited the questions to add links and images in manually.
I don't know how many other questions he or others have edited. Is there a way to mass-correct/remove these missing images?