For the above firmware versions the following snapshot URL works if you disable ONVIF authentication on the camera. the ONVIF username, password seems to be hard coded as admin, admin. So what's the point of having it enabled if your camera is behind a firewall.
http://192.168.1.22/onvifsnapshot/media_service/snapshot?channel=1&subtype=0
What in the world!? You can even log in to the snapshot by just going to http://IP:port/onvifsnapshot/ no matter what the security you have setup... how can I lock people out if I have this online?
(I have this firmware installed: DH_IPC-HX5(4)XXX_Eng_P_Stream3_IVS_V2.420.0000.12.R.20151021)