Hmmm, on this page, I can see the tile-like artifacting that IrfanView causes when expanding images beyond their original dimensions. That's why I initially added the "jpeg_artifacts" tag.
However, the image is actually intact (fine) when I save and open it locally. I therefore removed the tag. Does anybody see what I'm getting at?
I don't see the problem either. The issue may be that the image was encoded progressively (interlaced) and had only partially loaded. See second link for a visual example.
I have taken a screenshot of the downloaded image copy next to the embedded page image; dimensions are 1920x1080. VERY interesting: the page image is showing larger than the local copy! Normally in my experience, Danbooru only shows either the original size or a smaller version of a very large image - AFAIK, never larger-than-original.
Wondering if there is a sandbox area here I could upload to...?