You are both ( @uwelang and @trumpman) right and wrong.
Right in terms that for content from public domains, legally we are not compelled to provide attribution.
Wrong in terms of Cheetah bot here on Steemit, simply because the source is missing, and as such the article might be recognised as plagiarism even if it's not.
(And we have already seen some members being listed on Cheetah bot Black list for no real reason.)

For you @trumpman...
When I saw your reply that you've edited the post and put the new images, I really came here to give you a vote. And I almost did. In last second I noticed you are missing that crapy "source," and I knew you might be in danger when Cheetah bot is in question. That's why I told you that I saw you've changed the images, but still not credit it.

I thought it would encourage you to that final small last step to stay on the safe side. Unfortunately, it caused total counter-effective response from your side. You started yelling at me for no real reason. That's why I commented with plagiarism tag.

Again wrong, I thought it would ring the bell in your mind to put it there so I can remove that creepy tag. But instead, unfortunately, you started to insult me heavily.

So, let me ask you...

Do you really think, I would bother replying to your comments almost half day long (and despite the insults, you throw my way) if I don't think your content and contribution is worth???

And I'm not talking only about this article. Because of that even more, I don't think is worth a risk to get on some black list for no reason, and if nothing else lose days or even weeks and more to prove otherwise and be taken down.

I don't know how many accounts you've seen in those past three months being here that have been heavily downvoted with a completely ruined reputation for this or that kind of Steemit abuse, but in past year I've seen a lot of them. Some even managed to pass under the radar for quite some time not bothering for the warnings that came their way from people like me (who just wanted them to succeed and avoid trouble).

So, let me ask you one final question.

Do you really think it wouldn't be easier for me just to report you when I first came here, instead of still replying to you (and again despite the insults, you throw my way) if I really wanted to harm you in any way???