We don't need to regulate what flag reasons are used, but providing suggestions on how to flag and when not to flag is useful. Especially since a generic "quality check" reason is pretty useless, IMO, and something that deserves feedback on the flagger's record or a dmail if used on a bunch of posts in a day, or on a consistent basis. It's a waste of time at that point unless there's an error so egregious that anyone with two eyes (or less) could spot.
Otherwise we're wasting moderators' time and effort if they spend 5-10 minutes looking over a picture only to pass the buck to someone else who does the same thing. That's time which could've gone to approving new posts in the queue wasted, as well as the time of whoever might want to appeal the flag
Plus, flagging is supposed to be feedback per topic #13113 - without information on what needs to be corrected, that's worse than useless.
So a howto would be good - it doesn't have to be a thorough course, but at least it should provide basics beyond we what's in the flagging popup.