An image that has been edited by a third party to replace the original text (Japanese or otherwise) with a translation into English (or another language).
This regularly occurs in Comics and doujinshi, scanlated or otherwise.
Uploading hard-translated images is discouraged, due to image quality issues, typographical issues, and the difficulty of confirming the correctness of the translations (see topic #2590 for discussion). The original image should be uploaded instead, and the translations applied via notes. Non-original hard translations should be made children of the original images whenever the latter can be found.
Posts that are hard-translated by the artist themselves should be tagged Alternate Language instead.