How to repair Corrupted jpeg file that still get their thumbail done correctly?

I've got a bunch of photos that were on an SD card. Most of them are corrupted now, I cannot open them in any program (Gwenview, Gimp, on windows too...) But every file browser still can correctly make most of their thumbnail. for instance : I'm aware that the SD card is probably dying, so I already made a dd image of the sd card, on which I can work. So far, My searches led me to photorec which does not work in my case: it recovered 4 useless photos and as about two/third of my ~400 still have their thumbnail, I still hope to have most of those back. What Can I do? Any help appreciated :) PS: I'm on Kubuntu 20.04, I'm able to be root and I'm not afraid of the command line (but a graphical tool is still handy :D )