Oh, those are generated by WordPress, not by EWWW. Well, I say “by WordPress”, but WordPress by itself only generates 4 “resizes” like that, and you can finetune the dimensions for those under Settings->Media. The default sizes are thumbnail, medium, medium_large (not configurable), and large.
It generates those with a quality of 82, which may not be as high as you like it, so EWWW actually lets you increase the quality for those resize on the advanced tab.
Also on the advanced tab, if you scroll a little, you’ll see a section where you can disable some or all of the resizes. If you see more than the 4 I listed + the pdf-full size, then your theme or some other plugin has registered additional sizes for use in some other place, or to make things even more responsive.
So how do those get into your pages, instead of the original you uploaded, is possibly the next question. And the answer is via the srcset attribute that WordPress inserts automatically within any image found in your post/page content.
What happens, basically, is that WordPress takes a list of the resizes available, and adds all of them to this ‘srcset’ attribute (or some, I don’t remember the criteria off-hand). Your browser then gets to pick which one best fits the page and device size, which may very well not be the original image.
You can also manually choose from some of these sizes when you insert an image, and there may be a default there that I don’t recall also.
Hope that’s enough insight for you 🙂
