I have noticed that in the amateurmicrography/photomacrography forum, fellow members of this forum have been commenting on posts that they have already seen here. Though some might see this merely as the encouragement of a fellow forum member it has a distorted effect on the other posters of images of that forum, keeping them down the visible order.
I think that as a matter of courtesy if we have already seen and or commented on an image we should refrain from doing so again.
I have to second what Kurt and apo said.
If the other forum's comments stimulated my scientific curiosity and I wanted to comment on it, am I allowed to do so? If I comment again, would that comment put an otherwise excellent image from another memeber/thread, for example Charles Krebs's image, beyond people's notice?
Do I have to abandon my right of free speech, to obey some not-so-well-established "etiquette"?
I am not sure other members mind duplicated comments. I myself certainly don't mind, even if my own thread is pushed down by those comments.
Maybe 75RR can ask forum administrators and get back to us, if such "etiquette" is needed.