Posts where the image has been edited by a third party to replace the original text (Japanese or otherwise) with a translation into English (or any other language). This regularly occurs in comics and doujinshi, scanlated or otherwise. Posts that received a translation officially should go under "alternate language".
Uploading a hard-translated image when the original already exists on Danbooru is discouraged, due to image quality issues, typographical issues, and the difficulty of confirming the correctness of the translations (see topic #2590 for discussion). Non-original hard translations should be made children of the original images whenever the latter can be found.
For translation quality's sake, please refrain from uploading hard-translated posts wherever possible.