@hj @jonossaseuraava @takao I'm sorry, but I don't think we are talking about the same thing here.

The end user has a poor download speed=they need to wait for a big image to download. From where they are downloading said image doesn't really matter, since their poor connection is the slowest variable in any case. Meaning it doesn't matter to for example 500 kb/s user if the server has 1 mb/s or 100 mb/s speed, because they will be limited to 500 kb/s.

As for server side transcoding: It is better to serve already optimized photos. It is way easier to hand-optimize the size when uploading/sending the photo than guessing at the server side what parameters are appropriate for this image. For example forcing full-hd jpegs to computer generated png graphics. Or forcing a RAW to jpeg conversation with some batch tool instead of using darktable or rawtherapee or whatever to optimize the image and export to a sane filetype.