I am in the process of setting up a new site, and I would really avoid using plugins more then necessary. My problem now are media sizes. I am alsways compressing the images I upload beforehand, but obviously WP is generating multiple sizes upon each upload and these newly generated images are NOT compressed/optimized. I know there are plugins such as Ewww or Smush which do that, but as mentioned, I would like to avoid them. Problem is that if I generate these extra sizes myself and optimize them, I can upload them via FTP, but WP still does not register them in the library. I tried using WP CLI to import them, and this worked, but WP again created new sizes for all the images uploaded! Is there a way to compress all these sizes myself before uploading and then registering these in the library? Or any other way to achieve what I want w/o plugins?