I don't mind a single user asking more than one legitimate picture identification question at a time. While "legitimate" is hard to nail down, @Canina's post pretty much nails my feelings too. Those rules are somewhat subjective, but that's why we have close votes. Moderators need to be willing to lower the hammer, though. It seems there is considerable consensus that what happened in the past is unacceptable.

If we could agree on "legitimate" I'd be happy with that, but it's inherently subjective so I wondered whether an objective measure would help in the meantime. (I said one unanswered at a time, not just one at a time -- incentive to fix a question that isn't currently answerable instead of going on to post more like it.)

I think @Canina's post does a good job of describing the requirements for picture identification questions. I would rather judge each question on its own merits than artificially limit users to a certain number of concurrent questions, whether good or bad. The points in Canina's post are spelled out well enough that most of the bad ID questions we have gotten here would be clearly bad by any reasonable interpretation of those requirements. There will always be some on the edge that are judgement calls, but the problems we've had here recently aren't really near the line. For example, all 6 ID questions that popped up in the last 24 hours would all clearly fall short of the requirements. I'd hate to throttle users that do a good job asking good ID questions. If we ever get overwhelmed with good ID questions, then it might be time to reconsider a rate-limit.

These are good points, and I agree with Canina's proposed requirements.