When transferring images on commons from other projects a lot of people forget
to upload the fullsize version (and sometimes they ask for deletion of original
afterward leading to lost of the fullsize original image). Moreover, if someone
upload the fullsize version, it can lead to a duplicate entry, thing that should
be avoided in any database.
Mediawiki should be configurable to disallow uploading of this kind images. The
software should then detect the leading prefix for scaled down image
/[0-9]+?px-/ and warn the user he have to get the fullsize image from the
probably just change the name field to circumevent the protection. Maybe upload
image, compute an hash of it, warn the user, and prevent uploads of this image
for the next 24 hours.