Xvfb
Fleetingxvfb
connect to a running xvfb-run
xvfb-run --server-num 99 --auth-file ${TMP}/xvfb-authority xterm
Then make it available locally
xauth -f ~/.Xauthority merge ${TMP}/xvfb-authority xterm
Then connect on it to run your command
DISPLAY=:99 scrot
or
scrot -D :99