The "report missing information" form does not allow to upload any images if a cover already exists, so there's no easy way to transfer the correct cover to the volunteer librarians.

As a workaround, sending a link seems to work, but it requires uploading the image somewhere first if it can't already be found online. (This may be a bigger issue for non-English books, since alternative language editions seem to often end up with very random assignments, sometimes not even corresponding to the right book.)