The ID space for Imgur's IDs is 5 characters of alphanumeric characters. I noticed that i.sstatic.net has opted instead for 8 characters, while still supporting the 5 characters for images from the Imgur era.
I'm curious what the rationale is for the expansion.
I don't hold anything against the decision. But I am curious. I'd have thought it would have been simpler to keep things consistent. And the Imgur era images only consumed ~2.5% of the 5-character ID space (How much of Stack's imgur image-ID space has been consumed?), so to be honest I'd be surprised if dealing with collisions was a major concern.