Five upper/lower case alphanumerics give $(26+26+10)^5$ = 916,132,832 combinations. Are they being recycled? Are any or all imgur PNGs or GIFs in stackexchange going to expire? If so, how soon? I remember when I first learned that FedEx tracking numbers were being recycled constantly; I was shocked until I did the math, then shocked again when I realized a few more digits would have fixed that, then un-shocked when I realized that expiration was probably OK after weighing the tradeoffs. With only five character file names, these imgur files look like someone has already planned on eventual expiry.
update: The breakage of the link seems to have been temporary, i.e. it works now. But I'm still curious, are the imgur links we use in stackexchange supposed to be permanent?