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First thing I noticed when switched from Windows to Linux was, that Linux has no strict naming convention and no obligatory file name extensions like .bmp, .jpg, .exe etc. Therefore I can not tell by the file name itself its file format.
If all JPEG files on my file system had the .jpg extension, I could simply find all JPEG files by:
find / -type f -name "*.jpg"
But if it is not the case I am clueless how to find all JPEG files.