In T120867#1868448, @matmarex wrote:

Also, I'd like to be sure we're solving the right problem: the bad uploads are primarily copyvios, and not just out-of-scope, or otherwise? We have to forcibly educate the user about copyright, and not about what images are useful for an encyclopedia, or otherwise? @Yann, @Natuur12: You reviewed a lot of the uploads, is that right?

In T120867#1868364, @matmarex wrote:

@INeverCry I'm confused and I don't know what you're trying to say, sorry. Yes, it's clear that the uploads are all from the same tool (I elaborated on which tool this is and how it works at https://commons.wikimedia.org/wiki/Commons:Administrators'_noticeboard#Cross-wiki_uploads). But the tool only allows uploading files from the device, which requires the uploads to first download the file from somewhere, which would be silly of them to do if the file is already available as fair-use on their favourite Wikipedia. We're now wondering what to do to stop people from uploading the copyvios, without discouraging them from contributing files entirely. (Note also that I'm not an administrator at Commons, and I can't see any deleted files.)

In T120867#1868174, @matmarex wrote:

In T120867#1867407, @INeverCry wrote:

Most of the copyvio cross-wiki uploads I've seen and tagged for speedy deletion are fair-use images from various wikis. These are already marked as being copyrighted and usually have warnings to that effect. I wonder why this doesn't discourage more new users from uploading fair-use images to Commons...

The cross-wiki upload tool only make it possible to upload images from your computer/device. It doesn't allow upload by URL or transferring from other wikis. So if people are indeed doing that, they have to be doing it by saving the image and uploading the file.

If you have any examples handy, it'd be interesting to see what wiki does the image come from and what wiki the uploader is from. If both are the same, it would be pretty weird, since they should already be able to use the local images… It would be more reasonable if it's, say, people taking images from en.wp, uploading to Commons and using them on other wikis.

In T120867#1867426, @INeverCry wrote:

Is there any way to prevent images from being uploaded to Commons via cross-wiki uploading that are marked as fair-use on their respective wikis?

I don't think it would be possible:

• As I mentioned, the files come from the user's computer, and we don't know the "real" source when they're being uploaded.
• After the file is uploaded, we could search for duplicates on non-Commons wikis, but:
  • MediaWiki's duplicate detection only works for exact byte-by-byte duplicates (it's implemented by computing and storing SHA1 hashes of uploaded files, and comparing these). If the image is modified, scaled, watermarked, whatever, it won't match.
  • Even if we do find a duplicate, most wikis' metadata is a lot worse than Commons' and we probably couldn't reliably determine whether it's a fair-use image, or a free one that could be transferred, but was simply uploaded locally first.

I think this would work much better as a bot or Labs tool or something, that would flag these files to be checked by humans. (In fact, I'll be really surprised if there isn't one already.)

Is there any way to prevent images from being uploaded to Commons via cross-wiki uploading that are marked as fair-use on their respective wikis?

Most of the copyvio cross-wiki uploads I've seen and tagged for speedy deletion are fair-use images from various wikis. These are already marked as being copyrighted and usually have warnings to that effect. I wonder why this doesn't discourage more new users from uploading fair-use images to Commons...