The jpgrecovery command simply does not process this files.
The strings command finds an embedded string "_CONSOLE" !
If I open the file in a file viewer (shotwell, GIMP, Firefox, Google Chrome), I get the error that the file starts with 0 0, which is correct, as seen in the above hexdump.
Using identify from the imagemagick package results in:
20140207_142030.jpg JPG 0x0 16-bit sRGB 3.625MiB 0.000u 0:00.002
identify-im6.q16: Not a JPEG file: starts with 0x00 0x00 `20140207_142030.jpg' @ error/jpeg.c/JPEGErrorHandler/338.
All this commands were executed on Debian 12.
I have hundreds of files with this JPG extension and for each file the header is starting with 0 0 in this folder, so I assume the problem is not corruption of one file.
My questions:
What kind of file format is this?
How can I convert the files to JPGs?
Edit: Added the output of some suggested data/commands to questions
Edit: Mark as solved, thanks to @hades@hades@lemm.ee .
Thanks a lot to everyone helping to figure this out/pointing me in the right direction! <3