1. The poster ADMITS that he took the images from the website of the person claiming copyright, and that he DID NOT scan them himself.
2. The poster ADMITS that there are identical identifying marks (flaws, etc.) in both the images he took from the website claiming copyright, and from other websites, which he ADMITS probably got them from the website claiming copyright.
I think at this point it's best to give the advice often given by one of the moderators over on the Domain Names forum: some things are best not discussed in such concrete detail here. Posts = evidence.
I agree that the use of the term "stealing" in the post's title (quotation marks or not!) suggests that the poster knew the answer (at least to the "ethical" question) from the start...
Why not just concentrate on gaining access to source material, and not have this ambiguous legal issue hanging over your site? No, you may not get access to the same material, but perhaps some that is equally unique and valuable.
If my intuition is right, the poster does have a passion for the subject material. If he can respect the other site's equal passion, perhaps the two add up to more than the sum. Otherwise, what is he adding?