To be honest, a decent image server that can be the root server for a CDN and do the right things with modern web formats is something that should be standard and built in by now, with nobody needing to build and install their own.

That said, this is far better than my own non-existent image server.

For me a measure of quality is the rendered HTML code, which should use all the content sectioning elements and not be bloated with gazillions of divs and classes. This software is well off the pace in this regard.