From clicking around this site, it looks like their image dithering technique has taken away the color quality required to properly view the graphs on this article: https://solar.lowtechmagazine.com/2015/10/the-4g-mobile-inte...
I'm not convinced it saves much in the way of bandwidth, either. If you take this[0] image, it's 43 KB for a 800x533 image. I'd expect a JPEG to be able to do that without too much in the way of artifacts. It does give the page a kind of neat newspapery vibe, though. [0]: https://solar.lowtechmagazine.com/dithers/sps_wide.png
For example, looking at their response headers I see the image cache control expires after a day, plus has validation caching. This could be significantly improved. First, get rid of the `etag`, `expires`, and `last-modified` headers and go with expiration caching only. Increase the `max-age` from one day (86400) to one year (31536000). I get the HTML expiring after 24 hours, but images should be more aggressively cached. Validation caching always requires a round trip to the server, plus running validation rules on every single request so it can't save nearly as much bandwith and CPU as simple expiration caching.
Also, if they got rid of the those headers, plus the pointless `server: nginx/1.10.3` they could save over 100b per HTTP response. I counted 19 requests on that article, so it may seem small, but it can add up to a significant amount.