I'm thinking if stealing of infographics with or without a source is considered as plagiarism?
Without a source - definitely plagiarism. With a source - not plagiarism, but kind of scummy in my opinion.
Simply copy and pasting someone else's work, adding nothing of your own, and slapping a reference link on the bottom, whilst not plagiarism is pretty low behavior my opinion. You see it all the time across the forum; people posting entire news articles, blog posts, medium posts, etc., written by someone else, and not even adding a single sentence of their own thoughts. The same thing could happen with infographics, although it is much less common than the other categories I mentioned. Providing a source means they won't get banned, but I still think it's a pretty scummy thing to do and obviously only for padding post count and/or fishing for merits.
Edit: I accidentally a word
Copy pasting good work (and providing useful LINK) from people that could contribute to a place isn't that bad imo, just know where to post such things and where to avoid, but if I see a good thing on twitter or somewhere, then I rather copy paste + provide a link then turn around the words and make it something of my own...
To find something that could lead to an interesting discussion isn't that bad imo, when I do such things I also only do it where its appreciated...
Sometimes the posted thing could be a question as well, just to know how other respecter members thinking about that matter, so isn't it better to post it like that with a link rather then making it up yourself?