On the Metropolis website, static media was directly served from the uploaded version, which hwere usually unnecessarily larger and were not in a optimal format (e.g. PNG).
In order to speed up loading times, I developed this to transparently1 reduce bandwidth used. A quick search did not turn up a simple reverse proxy that I could put transparently (i.e. disables itself if not explicitly used) and has the least amount of features I need.