Why don't you use dbus to take a screenshot? Code: dbus-send --session --type=method_call --dest=org.nemomobile.lipstick /org/nemomobile/lipstick/screenshot org.nemomobile.lipstick.saveScreenshot string:/home/nemo/Pictures/screenshot_tmp.png
dbus-send --session --type=method_call --dest=org.nemomobile.lipstick /org/nemomobile/lipstick/screenshot org.nemomobile.lipstick.saveScreenshot string:/home/nemo/Pictures/screenshot_tmp.png