I don't know anything about websites so I have no idea how hard it would be to implement something like this but it definitely would be nice to have https://e621.net/iqdb_queries somewhere into https://e621.net/uploads/new as hyperlink or even incorporated as a whole. It's not having to find it (and only way I know it's through already posted image) and open is too hard but as I said it's just for ease and comfort.
So just my few cents.
Cheers.

I believe re621 has this feature, it shows duplicates while uploading, if it finds any.

It's been on the backlog for quite a while and should hopefully eventually happen. RE621 has the feature and I've came to rely on that quite a bit, unfortunately it only seems to work for me when a URL is provided rather than a file upload. I'm uploading from URL 99% of the time anyways so it's not a big deal.

m3g4p0n1 said:
I believe re621 has this feature, it shows duplicates while uploading, if it finds any.

re621 does get false positives from time to time (mostly with alts), but it's an absolute godsend. Highly recommended for all uploaders.

strikerman said:
re621 does get false positives from time to time (mostly with alts), but it's an absolute godsend. Highly recommended for all uploaders.

The false positives aren't exactly a bad thing either, if it's an alt version you can set that post as a parent/child of what you're uploading.

I prefer false positive than not seeing the same exact picture for some reason. I once put pic that I knew was superior version in tool on site and it didn't detect the one on site for some reason. Still no idea why.

I will probably check it later. Seems quite comprehensive. It's still additional something, though, and not everyone will use it. Thanks for mentioning it anyway.