supported cameras

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

webcam

Install v4l2loopback and enable it's module:

$ sudo vi /etc/modules
dslr-webcam
$ sudo vi /etc/modprobe.d/dslr-webcam.conf
alias dslr-webcam v4l2loopback
options v4l2loopback exclusive_caps=1 max_buffers=2
$ sudo reboot

Inspect your camera's supported features:

gphoto2 --auto-detect
    List auto-detected cameras and the ports to which they are connected.
gphoto2 --summary
    Summary of camera status.
gphoto2 --abilities
    Display the camera and driver abilities specified in the libgphoto2
    database. Use --summary to query an overview of the camera.

Find a dummy video device to use:

v4l2-ctl --list-devices |grep -A1 Dummy

Write your camera's display to /dev/video2:

gphoto2 --stdout --capture-movie \
  | ffmpeg -i - -vcodec rawvideo -pix_fmt yuv420p -threads 0 -f v4l2 /dev/video2