I've noticed that many new users are confused about how images work on this -- and other -- wikis. There's been many an occasion where I've seen a user upload two or even three duplicates of the same image.
Now, there already is a notice warning about duplicate images on the file upload page. I think it needs to be made more prominent. I also think that there needs to be more of a penalty -- obviously, we shouldn't ban someone the first time they upload an image, but I think that people who repeatedly upload duplicates after being warned should have their ability to upload files taken away (temporarily). Like, if someone tells a user to stop uploading duplicates (and/or why) and they upload four more, then a more formalized sanction should be administered.
That might sound a little extreme, until you consider the sheer number of unnecessary duplicates on this site. It's huge. Many times, I've seen a user upload a dupe, and when I click the image link to see what it's a duplicate of, I see five or six other duplicates -- often from several different users! Clearly, the current system (a barely-noticeable message above the form) isn't working too well.
This also ties in with what a lot of computer usability experts have found: when designing a website, don't even bother writing long explanations. Nobody will read them. It's human nature, when presented with a form, to skip all prose and immediately begin to fill out the form. There's no reason, however, for a user to ignore a warning message left on their social profile, which is why I've set that as the sort of "punishment precursor", the point at which duplicate uploads stop being a mistake and start being negligence.*
I'd also recommend a time interval -- don't give them four strikes after being warned, give them four strikes a week. I've seen even veterans upload dupes without noticing, which is why a time interval would be more appropriate (a rate, rather than a quantity). It would be ridiculous if someone made three duplicate uploads after being warned, and then spent two or three years becoming a super-experienced veteran, but then got punished for inadvertently uploading another duplicate despite the three-year gap between their previous mistake.
Thoughts? Suggestions? Ideas? Opinions?
* Wait, do notifications about profile comments show up anywhere? Or is it just the Main Page?