dcraw is an ANSI C program that decodes any raw image from any digital camera
on any computer running any operating system. It's become a standard tool
within and without the Open Source world. It's small (about 3000 lines),
portable (standard C libraries only), free (both "gratis" and "libre"), and
when used skillfully, produces better-quality output than the tools provided by
the camera vendor.

This version is modified to add auto-rotate to exported thumbnails, and also
add adjustment for camera timezone offset. If your thumbnails appear upside
down, set DCRAW_RTC env var.

WWW: http://www.cybercom.net/~dcoffin/dcraw/
WWW: https://dx.mehomi.com/autorot.html
WWW: https://dx.mehomi.com/photohack.html