It would shave off time from back checking images, as well as decrease the likelihood of duplicate images
This feature would effect the upload page, best type of link in my oppinion would be one that opens a new tab when clicking said link
I don't know if it is possible, but maybe if uploading a file choice automatically ran a harry.lu upon input on the selected image, telling users that said image is already on e621 as an alternative to simply having harry.lu as a linked option
If this feature is approved, maybe include a small tutorial on the file type one must use to check harry.lu to avoid user complaint on "incorrect filetype" notifications
Updated by savageorange