gPhoto (GNU Photo) is a command line tool for previewing, retrieving,
and capturing images from a range of supported digital cameras to your
local hard drive. It does not support digital cameras based on the USB
storage protocol, because those can be mounted by Linux directly. Find
the list of supported cameras at the following URL:

http://gphoto.org/proj/libgphoto2/support.php

or by running

gphoto2 --list-cameras