m0useanswered grow question 5 months ago It's always going to reprocess the image to make it work for the site it part of how it works, I don't think there is anything you can do even if you upload the specs the site uses.
If you upload the image in multiple sizes and the size reprocesses them all and they are all different sizes after the fact just upload whatever you got.
I process mine before hand and reduce resolution by 50% and add in watermarks and they get processed all the same when I upload em and I don't notice to much of a loss in quality.