imghdr.what failed to identify JPEG

[Arsenal]

Hi,

I have 206 jpg files. And imghdr.what returns 'None' for 52 of them,
and I found that actually those 52 files can be viewed perfectly with
an image viewer (xnview), and xnview also identifed them as JPEG
TrueColor(v1.1) in the File Properties.

Is it true that the jpg file format has more than one "identifying
signature" which the imghdr.what function didn't yet incorporate, and
hence the false negatives?

Thanks!