I'll give it a try. I am not an attorney. This is not legal advice. I have published nonfiction material which used copyrighted photos. I was absolutely required to obtain written permission from the copyright holder, which was granted, but under the condition that I acknowledge him in the caption. Print publishing and posting pictures on the internet, including social media, are handled the same way under copyright law. There are exceptions under Fair Use (reporting news, documentaries, critiques, commentaries, parody, etc.) that don't apply to your question.
Posting copyrighted images on the web is illegal without permission of the copyright holder. You can be certain that pics of celebrities are copyrighted, usually to a photographer, agency or publicist. Use of the photo without permission is considered copyright infringement. This also applies to any image that was altered via photo editing or AI. Also, celebrities have a right to their identity, image and likeness, even if they don't own the copyright. Even stories about celebrities without pics could be in legal peril. So, both the copyright owner and celebrity could both make a case.
Here's a hypothetical example. You post a titfight story about Britney Spears which includes a copyrighted pic. The photographer who owns the copyright finds out about it. What would happen? He/she would likely take action if the pic is being used for monetary gain, advertising, or promoting false information. Fortunately for you, none of these apply. The owner might find the content offensive. He/she would likely send a cease-and-desist order to the site, demanding the pics be removed immediately. That would likely be the end of it. Britney Spears finds out about your post. Again, you are not making money off the post, but she finds the pic and story highly offensive. She could have a legal case, claiming that the post caused her great emotional distress, humiliation, damage to her reputation or career. Not likely, especially from an obscure web site. She could send a cease-and-desist letter.
Practically speaking, the chances of any of this happening are extremely low. The internet is a sea of unauthorized pics and stories. Celebrities and copyright holders would need to find your post on FCF and care enough about it to take action. They have far greater concerns when it comes to the internet. Scarlett Johansson is suing a company that used her AI generated likeness and voice for an ad without her permission for monetary gain. Taylor Swift is threatening a lawsuit over AI generated sexually explicit photos that received 45 million views on X (formerly Twitter). Your worst nightmare would be if your story or fake pics go viral.
When you registered on FCF, I believe you checked a box that said, among other things, that you would not post unauthorized copyrighted material.