Different methods for grabbing an graphical image of what is being displayed on a physical or virtual device.

Linux

Grab all vt screenshots

for X in {0..10} ; do
  sudo DISPLAY=:0 fbgrab -c${X} fbgrab_vt${X}_screenshot.png ;
done ;

Screenshot X using scrot

sudo DISPLAY=:0 scrot -b -d 5 'scrot_%F-%T.png'

Screenshot X using imagemagick

sudo DISPLAY=:0 import -window root imagemagick_screenshot.png

macOS

screencapture screenshot.png

There are a lot of command line args for this tool.