Heyo, just some stuff I noticed that might be useful (or maybe it's old news already) that I didn't see on the wiki page. I don't want to edit it because I'm not fully certain about this stuff.
Tumblr:
Seems to be allowing images greater than 1280x again.
Example: https://maxpawb.tumblr.com/post/189856511246/junebug
If you just right click -> view image, you'll be taken to the standard 1280, but if you left click a significantly larger image pops up. This only seems to apply to posts made a month or two ago and to my knowledge is not retroactive.I use Image Max URL addon for Firefox and it doesn't catch that particular redirect. ("Image Max URL works by replacing URLs, and in some cases, querying website-specific APIs.")
DeviantArt:
Possible way to get a higher resolution.
Example: https://www.deviantart.com/nik159/art/Worlds-best-rabbit-officer-824111949
Clicking the little + magnification icon takes me to a highly compressed 71 kb version [I'd put links here, but these appear to be temporary links that expire quickly], but the addon I mentioned earlier redirects me to a 1302 kb version of the same resolution, but with far less compression artifacts. I'm assuming this is that API query thing they mention; I'm not really code savvy. This is nowhere near the original (inaccessible) file, but it could be useful if the artist does not allow downloads and there are no other sources.A note of caution though, the redirects seem a bit finnicky and on rare occasion redirect to an image of worse quality.
Anyways, that's about it; just throwing some info out there in case someone finds it useful.
Updated