I was always taught that direct copying of another source is plagiarism, even if the source is properly referenced. I've seen this a few times in answers here but, at the same time, I also understand that we're not writing formal publications. Is there an official stance on this?
Plagiarism is not allowed here, and entirely plagiarized posts are subject to deletion.
The rules here are the same as for academic publications, all sources have to be cited and quotes must be marked in some way to indicate that those parts are quoted, and not your own words. The best way to do that is to put the text in blockquotes.
The source of images also must be cited if you didn't create them yourself.