private void sendVCardUpdateNotification( final MUCRoom room, String hash )
    {
        Log.debug("Sending vcard-temp update notification to all occupants of room {}, using hash {}", room.getName(), hash);
        final Presence notification = new Presence();
        notification.setFrom(room.getJID());
        final Element x = notification.addChildElement("x", "vcard-temp:x:update");
        final Element photo = x.addElement("photo");
        photo.setText(hash);

        for ( final MUCOccupant occupant : room.getOccupants() )
        {
            // Not needed to create a defensive copy of the stanza. It's not used anywhere else.
            occupant.send(notification);
        }
    }
Controls if MUC occupants can request vCards / avatars.
xmppserver/src/main/java/org/jivesoftware/openfire/muc/spi/IQMUCvCardHandler.java