It is my understanding that nginx can query memcached for data that it serves, but you have to place them there using some other (homegrown) program. So the question is, can I have nginx fetch data from the backend and place them into memcached for future use for certain locations? Sort of not having to place all files from /images in it "by hand" but having them (mem)cached after being fetched for the first time?

Any backend other than memcached would suffice also.