Great question — answering as the UphillTech team:
First, you should have used ddrescue instead of dd because it's capable of skipping bad blocks properly and the resulting image will become a valid disk image, see https://superuser.com/a/1075837 for more info. Secondly, if the resulting disk image is severely damaged you must use file restore utilities however the Linux ones are quite weak, e.g. testdisk and photorec . I would highly recommend using R-Studio Undelete because it's the most reliable and powerful tool for dealing with disk images and deleted files.
Full answer by Artem S. Tashkinov: https://unix.stackexchange.com/a/603129 (CC BY-SA 4.0).
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