A post that is completely identical to its parent down to the pixel and was either posted after another post with the same Pixel Hash or has no source while their parent does, and thus is inferior for Danbooru purposes.
If a PNG with a vastly larger filesize to a JPG is a pixel-perfect duplicate, lossy-lossless may also apply.
Pixiv and Twitter posts are often identical, even if they have different filesizes. In 2019 Twitter stopped compressing as harshly as they used to and in late 2020 Pixiv started losslessly recompressing their JPGs to strip metadata, so typically if there's only a few KBs of difference between two identical pictures from these two sites, it means they're the exact same image.
There are three ways to know if similar images are pixel-perfect duplicates:
On the upload page, a red pixel-perfect duplicate label will show at the bottom. Clicking the label will redirect to an existing post.
On the image's asset page, clicking on Pixel Hash will show other posts and assets with the same Pixel Hash. These are pixel-perfect duplicates.
An image's asset page can be opened by clicking on the text below the image in the uploader showing the filesize, file type and resolution or by clicking the two arrows beside the resolution on a post's page.
For uploads already posted, the post with the lowest id should be the parent, and the rest should be tagged as pixel-perfect duplicate and parented to it. The only exception is if the post with the lowest id has no source, which then the next highest id with a valid source should be the parent.
This tag is automatically populated for new posts unconditionally and should not be removed by users except to dispute incorrect additions of the tag pursuant to the above guidelines. In general, uploaders should avoid posting duplicates. For duplicates already posted, uploaders are responsible for properly tagging and parenting their duplicates to the existing post.
Do not flag posts just because they are under this tag if they come from a first-party source.
