I have unmixed fellings about this: people who are not logged in should not be able to upload. People are spending very valuable time on removing illegitimate uploads so we should be very strict on this. I would even suggest the rule that unused pictures are fair game. Being able to check this is not a nice-to-have but a must-have. If we cannot integrate the different Wikipedias enough to do this easily, then we should decide that each gets its own upload space. Disk space is cheap, the time of contributers is certainly not.

There's two issues there: as for upload privileges, those in favor of restricting them to logged in users make a good case, so I'll make that happen soon.

The second issue is should the Wikis share uploads. I'm of the opinion that each Wiki should be an island unto itself, both conceptually and physically. Images are conceptually "inline" content, even though they are implemented as external links for technical reasons. Isolating them for each wiki and making all links internal makes it possible to encapsulate them, say, for a CD, or for backup. The combination of database + upload directory should be able to reproduce a Wiki in its entirety. I would even go so far as to say that eventually, inline-rendered external image links shouldn't be allowed--they should be treated like all other external links rather than being rendered.

If that means having to upload flags 20 times, sobeit. There might be good reasons for some Wiki to want to use different flag images anyway.