pixel-perfect duplicate
This tag is automatically populated.
Posts under this tag are perfectly identical pixel by pixel to their parent, and were either uploaded afterwards or have no source while their parent does, and thus are inferior for danbooru's purpose.
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 same exact image. See the Word of Caution paragraph on the howto:twitter wiki page.
Do not flag posts just because they are under this tag if they come from a first-party source.
In case you want to check if two similar images are pixel-perfect duplicates, you can use this website (also supports pixiv urls).