gPhoto (GNU Photo) is a set of libraries 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. Those can be mounted by Linux directly.
As of this time, gPhoto supports around 1700 cameras, listed on:
http://gphoto.org/proj/libgphoto2/support.php
or by running
gphoto2 --list-cameras