We use an 'official' utility /usr/sbin/dsmetool to turn on/off the launch of standard camera.
Catching the cover open/closing:
bool ret = QDBusConnection::systemBus().connect(QString(),
DBUS_LENS_COVER,
"org.freedesktop.Hal.Device",
"PropertyModified",
this,
SLOT(lenscover_property_modified(int, QList<Property>)));