Hey @Rozza,
You’re almost right.
Inspecting a traffic for an image uploader shows that first it uploads the image (POST request I guess in Base64 encoding which means that the amount of data transferred is larger than the image).
On the 2nd step the image is returned back to the app. BUT I don’t see any size optimizations here (not sure if they were before?).
Original image size is 2.3 MB, and the same one is returned (you see no options after “?” in the URL on the left).
There is no surprise image uploads work very slow 
As a side note: according to my knowledge it is possible to create a component which reduces image size before uploading for the native apps, though it might be more difficult to do this for webapps. Though I’ve never seen such component developed by anyone 
Best,
Victor.