Set up source type as remote
protocol as HTTP
remote method as Simple
remote host name ip address of Motion server ie 192.168.1.11
remote host port as 8081 ( providing this is the streaming port on Motion )
remote host path as /
set the colour and image size to match that of Motion ( found in the motion.conf file )

Hope this helps you or others.
https://forums.zoneminder.com/viewtopic.php?t=20575