I'm the type who always love to add images to my conversation, just as a wise man once said (i.e A picture/image is more than a thousand words), as it add colour to the conversation and makes it interesting to read. So in regards to this your question you just asked if is it permitted to post an A.I generated image on the forum, I will say "Yes", but, inasmuch as the A.I generated image connects and add value to the thread/topic of conversation, and "NO" that is, if the A.I generated image do not in anyway connect with the topic of discussion. Because just as Sir mprep made mention about how plagiarism is not applicable to image posting, it still doesn't mean there are no rules guiding image when posted in an off-topic.

Hence, if only you will be able to use such images to add quality/value to forum discussion, then I think you are good to good.