Re the existing rule quoted here;
"Do not post the same image in multiple forums or in multiple posts. The end result will most likely be one of the threads being deleted by a moderator."
That rule, though less clear now, was written long before POTN became filled with the "post your xyz images here" threads, which are now the bulk of all posts on the forum.
If you read closely though, as I said, it's not so clear. It was meant to prohibit posting multiple new threads started in multiple forums with the same images. The hint being "the end result will most likely be one of the threads being deleted "
It was never meant to prevent sample images from being posted in eg: lens thread, body thread, or subject thread, largely because at the time that sort of thread was not even remotely common on the forum. Times have changed, when this was written, the vast majority of image threads and traffic were begun with a members new thread of their images/adventure. These threads still exist, but they quickly disappear below the these newer public invitation to post threads.
I don't say any of this to dismiss the complaint, it is a valid one. One image does not need to be, and should not be posted in, the 100-400mm thread, the 7D2 thread, the birds pooping thread, and experimental, etc. I definitely empathize with any members sense of order and impulse control.
On the other hand, if this sort of posting is what now makes up the bulk of the forums traffic, if we do re-write the rules to exclude it specifically, and then start to crack down on it, what effect will that have on the forum membership and participation? What a shame to potentially chase off some of our most prolific members, who are decent people, over this.