Firstly, hash checks are not the same as image recognition. Image recognition works by converting pixel data into a function. Minor changes like resizing, slight blur or sharpening and color change will still mark the image as a duplicate since it remains within the threshold value. This basically clears most methods used to avoid detection.
Asking the original owner for authorization is somewhat complicated. Imagine permanently losing an old account with lots of uploaded clothes and you decide to reupload them to a new account or a group. You’ll have no way to confirm whether or not these clothes belong to you. Adding onto that, it would be easy to spam someone’s messages. Roblox should be able to handle this on their own, with some kind of a “dispute moderation” button being present to allow the uploader to explain why it is a duplicate. I’d bet this will stop practically every bot account and most re-uploaders.