gtkam is a graphical front end for the gphoto2 library. It does not communicate directly with the camera, but uses gphoto2 to do so. As a result, it is necessary to have gphoto2 installed and running correctly before gtkam will work.
This video show how I install and run GtKam on Raspberry Pi 2, connect and remote control Nikon DSLR D7000, and capture photos.
In this video, I install the current Raspbian supported package gtkam 0.1.18-1, not the latest version.
Once you plug in and power on your camera (D7000 in my case), you have to unmount it before GtKam/gPhoto2 connect it, otherwise it will fail with error of "Could not initialize camera".
With GtKam run properly, you can view camera's photos, capture photos, and save photos to RPi local storage...but may be too slow:(
reference: Quick start - Using gtkam
The NEW Raspbian Jessie provide apt-get gtkam 0.2.0, the latest version.