I've pushed an update to the image handling so they are now served using the WebP format if the requesting browser supports it. Currently that is Chrome, Opera and Android Mobile but Safari is adding support in the next version and there's hope that Firefox and Edge will get on board soon.
WebP is a newer image format that can replace Jpeg, Gif and Png but with much better compression rates for the same quality. Savings of 30-50% or more are typical (even more for many avatars). So images should download faster and consume less bandwidth. Coupled with the auto scaling on the client (which requests the appropriate size to fit the device being used) it should be especially useful for mobile users.
I don't have the animated Gif to animated WebP completed yet so they may not show up - the plan is to eventually serve a static image with a 'play' button so the user can decide whether to view what could be a large file (some animated Gif's are often 2Mb or more which you probably don't want on your cellphone).
More major speedups and savings for general topic-viewing on mobile is still to come ...