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How is this a pixel-perfect duplicate? If I download both images, strip away the metadata using exiftool -all= -api largefilesupport=1 -overwrite_original -progress -recurse image.png, the images end up with different size. MD5 hashes are also different.

Pixel-perfect duplicate is about the pixel hash not the MD5, meaning, when the pixels of the image are hashed together, they are the exact same. Metadata has no relevance here - if the upload page says it's a pixel-perfect duplicate, it means it's exactly identical to an existing image. Read the wiki for more information.

https://danbooru.donmai.us/media_assets?search[pixel_hash]=8d44cded249096a6f0e8866cc51415c1

GreenButterfly said in comment #2636157:

How is this a pixel-perfect duplicate? If I download both images, strip away the metadata using exiftool -all= -api largefilesupport=1 -overwrite_original -progress -recurse image.png, the images end up with different size. MD5 hashes are also different.

Stripping metadata does not account for compression methods. If you run both images through oxipng with oxipng --strip all --force image.png you get the same md5 hash for both.

I see. Thanks for the explanation. I "highly doubt" that I want to contribute to a website whose moderators immediately assume malice though. Have a nice day.

We had the upload page updated particularly to point out potential upload problems more clearly. When you're on the upload page of a pixel-perfect duplicate, there is a red label at the bottom and a warning notice below the post button that says "Exact duplicate of [post here]" along with a help page linked explaining what a pixel-perfect duplicate is.

The information is highlighted all there for you to help you avoid this and you still uploaded six of these, meaning you disregarded the warning which you could've asked about. We have a lot of people who intentionally do this exact thing - so I do apologise if that wasn't what you were actually doing and that you had somehow didn't catch that duplicates should try to be avoided. It really helps out to read help pages like help:upload before getting started.

Unless you're posting so fast that you don't have time to see the warning on the page, most people will catch the duplicate warning before posting, so posting them isn't really a matter of an accident but either doing it intentionally or not understanding that it should be avoided if possible.

FYI this is the algorithm for pixel hashes, TL:DR it normalizes the image's colorspace, channel count etc, then writes it out as a .pam file, and takes the MD5 for that. It's different for non-images, but in all cases it's written in a way where you can expect no false positives (barring accidental MD5 collissions but you have to be really unlucky for that).

this is so hot

I thought it was Hina and Sensei was repeatedly getting her horns stabbed into his thighs