Images posted to Stack's imgur space have the following URL structure:
This implies to me that images stored there have a five-character ID, with at least 62 possible characters at each position in the ID. So, that gives around a billion unique IDs.
I've been curious for a while now: what fraction of these IDs are now allocated? How rapidly is this ID space being consumed? Per questions, e.g., here and here, there is (or was) no garbage collection implemented to scrub "dead" images, so at some point there's presumably going to be a crunch on new IDs.
How close are we to the point of exhausting the imgur image ID space?