4chan recently enabled something that affects image quality, and there is a workaround to get full resolution. There's a discussion archived here: https://desuarchive.org/trash/thread/62965488/

Obviously, anonymous imageboards are not a good source to begin with. But sometimes things are posted in drawthreads there and nowhere else, and there's a lot of results for source:*4chan*, so it's relevant to some. I don't have time right now and it feels a little presumptive to do it myself without discussion, but hopefully someone can distill this information into https://e621.net/wiki_pages/16162 which currently doesn't have an entry for 4chan at all.

arrow189 said:
4chan recently enabled something that affects image quality, and there is a workaround to get full resolution. There's a discussion archived here: https://desuarchive.org/trash/thread/62965488/

Obviously, anonymous imageboards are not a good source to begin with. But sometimes things are posted in drawthreads there and nowhere else, and there's a lot of results for source:*4chan*, so it's relevant to some. I don't have time right now and it feels a little presumptive to do it myself without discussion, but hopefully someone can distill this information into https://e621.net/wiki_pages/16162 which currently doesn't have an entry for 4chan at all.

Damn, see also: ImgUr posts on boards. This is why I started archiving sources like that when I can.

4Chan is a bit more complicated because it's often one of the thread archive sites or a 3rd-party domain like ImgUr.com