Commons is seeing a large number of files uploaded via the cross-wiki upload dialog that are copyright violations. In order to fix this, we could...
* On clicking "Upload", bold the license requirement, and add another message saying "Be sure, now"
* Require the user to type the string "I understand that I must be the owner of the copyright on this image in order to upload it" into a text box to confirm
* Clarify what "copyright owner" means, something like "Did you take this picture? Did you draw this drawing?" etc. etc.
Beware of copying the UploadWizard process. Too bulky.
We ran an A/B test of four different interface options. They weren't very successful. https://www.mediawiki.org/wiki/Multimedia/December_2015_cross-wiki_upload_A/B_test
We're working on a second round now.