I don't know if anyone has any suggestions to deal with this kind of problem, or even if it has already been recognised as an issue. The non-technical answer is, of course, to copy the commons images to the local wiki, but that kind of defeats the point of commons, doesn't it?
- Mark Clements (HappyDog)
It's commons policy not to delete images as long as the images are used anywhere, if the deletion is not urgent (copyvios and policy-vios can be deleted right away). Some people don't seem to get that into their head, though.
Note that commons admins often rely on my CheckUsage tool to check where an image is used. Due to the way to database is fed from the parser, this might miss some uses, though. Specifically, it may miss any ''conditional'' use of an image, i.e. used directly or indirectly inside a {{#if}} or {{#switch}} clause.
-- Daniel