(I only started thinking about this after the DDoS debacle, so apologies if this is considered a necropost.)
I wanted to add some thoughts about reduced picture size in case this feature request gets picked up in the future.
Since it would obviously be too CPU-intensive on the servers to downscale on-demand, it would probably have to be done by caching downscaled copies of the chapters and serving a particular quality based on user preferences. It might make sense to have, say, 3 levels: low - for mobile, high - for desktop, original - for purists.
If downscaling all chapters server-side after upload is too enormous or expensive a task, maybe this feature could be supported in a best-effort manner by allowing willing scanlators or community members to upload multiple versions of their chapters at the various quality levels, with image quality metric and/or file size checks implemented to run (client-side in the browser?) prior to upload. The admins and community could work out the quality levels to support and the requirements for each, and propose best-practice downscaling algorithms and settings for uploaders to use.