Get md5 or something to check if there is duplicates; on your account and / or on the whole site. At times the site manages to load the same image 10 times, and takes forever to delete again.
Dropbox does it. But then it usually shows you a virtual file on their servers. Imgur links are direct. I am not sure if it is possible for Imgur to have one file with multiple URLs easily.
Duplicates are one thing - reposts are another. Perhaps a matching engine like TinEye could be helpful to prevent reposts of images stolen from elsewhere.... (not that there's anything wrong with that)
It would be nice to detect any duplicates and automatically bring the old posting back to the top. If someone found an old posting interesting, it may be worth revisiting. At the same time, the original poster gets the credits for bringing it up weeks or even years before. Reposting is not a crime, but treating it as new is.