The only way I'd know how to do this is to pull from Google capcha.
https://developers.google.com/recaptcha/docs/display
You would have to change the upload button to go to a webpage to validate then send you to the upload code webpage. So each folder would have a capcha.html and a hfs template of the upload code...
https://developers.google.com/recaptcha/docs/display
You would have to change the upload button to go to a webpage to validate then send you to the upload code webpage. So each folder would have a capcha.html and a hfs template of the upload code...