This question probably belongs to some more general meta but since most heavily I use links on MO let me still ask it here.
Occasionally I link to materials which may disappear at some point - like an image found at some obscure place or an unpublished note on somebody's page at the current affiliation place which might change. While an image I can always just download and then upload, I wonder whether there is a quicker way to do it, and for other cases I don't know at all what to do.
I've heard of the terms "stable url", "persistent link", "permalink" but I don't know much about it.
Is there a way to use links on MO that would not expire?